












PRESENTED BY 



















Manufacture of Soap 


By 


LINCOLN BURROWS 

ii 

MANUFACTURING CHEMIST 


MANUFACTURE OF SOAP 
Parts 1-3 



394 


Published by 

INTERNATIONAL TEXTBOOK COMPANY 

SCRANTON, PA. 

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Manufacture of Soap, Parts 1, 2, and 3: Copyright, 1923, 1909, 1902, by Interna 
tional Textbook Company. 


Copyright in Great Britain 


All rights reserved 


Printed in U. S. A. 




International Textbook Press 
Scranton, Pa. 


80049 










JH'T'K- \S 


CONTENTS 


Note. —This book is made up of separate parts, or sections, as indicated by 

their titles, and the page numbers of each usually begin with 1. In this list of 

contents the titles of the parts are given in the order in which they appear in 

the book, and under each title is a full synopsis of the subjects treated. 

MANUFACTURE OF SOAP, PART 1 

Pages 

Introduction . 1- 3 

Definition of soap; Classes of soap; General outline of 
the manufacture of a settled soap. 

Raw Materials of Soap Manufacture. 4-63 

Animal Soap Stock. 4- 5 

Manufacture of Animal Soap Stock... 6-7 

Vegetable Soap Stock. 8-27 

Cottonseed oil; Cocoanut oil; Palm-kernel oil; Corn oil; 

Olive oil; Red oil; Lime-saponification process; Acid- 
saponification process; Aqueous-saponification process; 

Twitchell process; Rosin. 

Alkalies and Their Manufacture. 28-49 

Le Blanc process of manufacturing sodium carbonate; 

Solvay process; Castner electrolytic process for the 
producion of caustic soda and chlorine; Grading of 
soda ash; Grading of caustic soda; Preparation of 
caustic-soda lye; Caustic potash; Measurement of the 
density of liquids. 

Chemistry of Soap Manufacture. 50 

Glycerides and Their Properties. 50-53 

Behavior of Fats and Oils Toward Saponifying Agents 54-433 

MANUFACTURE OF SOAP, PART 2 . 

Processes of Soap Manufacture. 1-65 

General Remarks . 1 

Manufacture of Boiled or Settled Soaps. 2—54 

Boiling-room processes; Soap kettle; Stages of saponi¬ 
fication; Graining the soap; Rosin changes; Filling 
the soap; Crutching the soap; Soap pumps; Filling 
materials ; Finishing-room processes. 

Semiboiled Soaps. 55-57 

Cold-Process Soap . 58-65 















CONTENTS 


IV 


MANUFACTURE OF SOAP, PART 3 

Pages 

Remelting of Soap. 1-3 

Manufacture of Toilet Soap. 4-21 

Milled-Process Soap . 4—16 

Perfuming of Soap. 17-18 

Coloring of Toilet Soap. 20-21 

Manufacture of Soap Powder. 22-24 

Recovery of Glycerine From Waste-Soap Lye. 25-41 

Manufacture of Glycerine. 25-32 

Treatment of Crude Glycerine. 33-41 

Chemical Examination of Raw Materials and Products 42-69 

Examination of Soap Stock. 43-57 

Samoling; Titer test; Wijs method for determination of 
iodine value; Analysis of rosin; Analysis of soda ash; 

Analysis of commercial caustic soda. 

Routine Chemical Examination of Kettle-Room 

Products . 58-63 

Analysis of waste soap lye; Acetin method; Bichromate 
oxidation method. 

Soap Analysis and the Interpretation of Results.64-65 

Chemical Examination of Refined Glycerine. 66-68 

Specifications for Glycerine. 69 
















MANUFACTURE OF SOAP 

Serial 2055A (PARTI) Edition 1 


INTRODUCTION 

1. Definition of Soap. —Soap, strictly speaking, is the 
compound of an alkali, either sodium or potassium, with the 
higher fatty acids, especially with oleic, palmitic, and stearic 
acids. The insoluble compound of a fatty acid with a heavy 
metal is, however, technically called a soap. The chemist is 
familiar with the lead soap or lead plaster of the pharmacy, 
with alumina soap used as a thickener of lubricating oils, and 
with iron and chromium soaps used in dyeing and in the color 
printing of textiles. 

As commonly known, soap is, according to its quality and 
the use for which it is intended, a mechanical mixture of the 
compound just described with varying proportions of water, 
with soluble alkali compounds of the rosin acids, with sal 
soda, NazCOzlOHiO, with sodium silicate or soluble glass, or 
with other inert, detersive, or odoriferous agents, incorporated 
for the purpose of cheapening the product, improving its 
appearance, increasing the detersive action, or overcoming 
the natural odor with an agreeable perfume. Therefore, 
commercial soap is a mixture of pure soap with a diluent, as 
water; with body-imparting substances, as talc, starch, or a 
petroleum residue; or with detersive agents in aqueous solu¬ 
tion, as sodium carbonate, borax, or sodium silicate. These 
additions may all be present in a single soap, but the nature 
and amount of the additions present depend on the character 
of the soap itself and on the purpose for which it is intended. 


COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED 



2 


MANUFACTURE OF SOAP, PART 1 


2. Classes of Soap. —There are three general classes of 
soap, namely, industrial, household, and toilet. In the 
first class are included so-called textile soaps used in the 
process of manufacture of cotton and woolen goods. In 
the second class are included the soaps that are consumed 
in various qualities and conditions by the laundry trade; 
and in the third class shaving and medicinal soaps may 
conveniently be included. The manufacturing of soap 
powder, scouring powder, and glycerine is generally associated 
with the soap industry. 

The discussion of the subject that follows will deal with 
the process of manufacture rather than with the use for 
which the product is intended. 


GENERAL OUTLINE OF THE MANUFACTURE OF A 

SETTLED SOAP 

3. The following outline gives a general idea of the 
various operations performed in the manufacture of a settled 
laundry or domestic soap. The relation of the different 
operations to one another is here made clear, and the follow¬ 
ing detailed descriptions of the different operations and 
processes rendered more intelligible. 

Source of Fatty Avoids .—In the definition of a soap just given, 
it was stated that a soap is a salt formed by the union of an 
organic acid of the higher fatty series with a metal, usually 
an alkali metal. The acid portion of soaps is derived from 
various animal and vegetable fats and oils, which are com¬ 
pounds of the organic acids just mentioned with glycerine. 

Soap Stocks .—Any fat or oil used in the manufacture of soap 
is called a soap stock, and may be of either animal or vegetable 
origin. The various kinds and grades of soap stock used will 
be fully discussed later. 

Saponification .—The operation by which oils and fats are 
combined with the alkali metals sodium or potassium to form 
soaps is called saponification. Technically, this term has a 
wider meaning, and applies to any operation that brings 
about a separation of an organic acid from an organic base. 



MANUFACTURE OF SOAP, PART 1 


o 

When an animal or a vegetable fat is boiled with a caustic 
alkali, a double decomposition takes place. The products 
are the alkali salts of the organic acids of the fats and glycerine. 

Graining and Settling. —After the saponification is com¬ 
plete, the soap is grained , or brought into a somewhat gran¬ 
ular condition, by the addition of certain salts or alkalies in 
whose solutions the soap is practically insoluble. When in 
this granular state, the soap separates from the impure 
liquor, or lye, which may be drained off. 

Crutching. —The soap, after the preceding treatment, is 
introducted into a machine called a crutcker , where it is 
crutched, or stirred, until it is thoroughly mixed. Here, fillers, 
perfumes, etc. are introduced and incorporated into the soap. 

Framing. —From the crutcher the soap is run by gravity 
to a rectangular box, called a frame , of proper dimensions, 
in which it is allowed to stand until it is of a consistency suit¬ 
able for cutting into slabs and bars. 

Slabbing. —The mass of solidified soap from the frame is 
first cut horizontally into slabs. This operation is called 
slabbing and is performed on a machine called a slabber. 
These slabs in turn are cut, on somewhat similar machines, 
into blocks of suitable dimensions for making finished cakes. 

Drying , Pressing , Etc. —The rough blocks are now dried 
superficially until a thin skin is formed over them. They 
are then pressed into finished cakes in dies and wrapped and 
packed for shipment. 


4 


MANUFACTURE OF SOAP, PART 1 


RAW MATERIALS OF SOAP MANUFACTURE 


Animal soap stock 

4. Animal soap stock occurs on the market in a variety 
of grades, depending on its origin and method of preparation. 
This stock constitutes the chief fatty material used by the 
soap maker. According to the part of the animal from 
which it is obtained and the method of rendering, it may be 
classified as tallow, bone stock, and grease. These classes 
of animal soap stock may again occur in various grades. 
In determining the quality, buyers, as a rule, depend on the 
simple tests of color, odor, and grain, supplemented by the 
titer, or hardness test, which will be described later. In 
addition, the percentage of moisture, unsaponifiable matter 
and the percentage of free fatty acids are determined. The 
last determination is of especial importance when the stock 
is considered with relation to its yield of glycerine. 

5. Tallow. —The tallow used in soap making varies in 
its composition according to the part of the animal from which 
it is obtained and the nature of the food used in fattening the 
animal. Corn-fed cattle produce the firmest fat. The fat of 
mast-fed cattle is not so firm as that obtained from animals 
fattened on oil cake. Tallow consists of stearin, olein, and 
palmitin. 

6. The percentage of free fatty acids is not only a reliable 
index of the quality of the stock used by the Tenderer but 
is a telltale on the care that he has employed. The follow¬ 
ing conditions conducive to the formation of a high percent¬ 
age of free fatty acids in the various grades of tallow may 
be enumerated: 

1. Allowing the raw material to stand before rendering, 
especially in warm weather. After the death of the animal, 



MANUFACTURE OF SOAP, PART 1 


5 


decomposition immediately sets in, and the first step in the 
decomposition of tallow is the separation of the fatty anhy¬ 
drides from the glycerol, which is immediately followed by 
the decomposition of the glycerine and its loss as such. 

2. An excessively high temperature in rendering tends to 
increase the percentage of free fatty acids. The presence 
of water in the tissues and the influence of the high temperature 
in the rendering tank tend to the hydrolysis of the glyceride. 

3. Rendering in closed vessels increases the percentage of 
free fatty acids. It will be clear that conditions prevail here 
that are purposely introduced and maintained in the process 
for the saponification of glycerides with steam under pressure in 
the manufacture of fatty acids and glycerine. 

4. The season of the year has a great influence on the 
percentage of free fatty acid in even high-grade tallows, as 
the table given herewith will show. These figures are taken 
from a whole year’s consumption of the best average tallows 
used in a factory making a high-grade laundry soap. In 
determining the value of a tallow the season of the year must 
always be taken into consideration in respect to the free fatty 
acid. 




Free Fatty 



Acids 

Month 

Lots 

Per Cent. 

January.. 

.58 

4.31 

February. 

.55 

4.09 

March . 

.61 

4.27 

April. 

.63 

5.28 

May ... 

.47 

5.36 

June. 

.63 

6.39 

July . 

.53 

8.03 „ 

August. 

.81 

8.19 

September. 

.68 

7.28 

October. 

.63 

7.01 

November. 

.54 

5.12 

December. 

.75 

4.58 


The significance of the free-fatty-acid determination will 
be fully shown when the various fats and oils are discussed 














6 


MANUFACTURE OF SOAP, PART 1 


with reference to their content and yield of glycerine and 
the changes incident to saponification. 

7. Bone Stock. —Bone stock is intermediate in quality 
between tallow and grease and is obtained from fresh bones 
by rendering in a closed vessel under pressure. 

8. Grease. —The commercial term grease is applied to 
all fatty material of animal origin that cannot be classified 
among such distinctive products as tallow, lard, etc. It is 
obtained from hides, kitchen refuse, recovered garbage, offal, 
dead animals, etc. 

White grease is made directly from hog fat and trimmings 
and has a large use in the manufacture of white toilet soap. 
Owing to its high percentage of olein it produces a soap much 
softer in body but with better lathering qualities. Dark, or 
house greases, as they are called, produce a much darker soap 
and are used mainly for soap powder soaps. With dark 
greases a boiling process and not a cold process should be 
employed, however, because it is necessary to remove the 
dark coloring matter and other impurities with the waste lyes, 
and also to eliminate all disagreeable odors. 


MANUFACTURE OF ANIMAL SOAP STOCK 

9. In the manufacture of animal soap stock the various 
grades of tallow are extracted from the fat-enclosing tissue 
that surrounds the intestines, muscles, and other organs of 
the animal. The feet yield neatsfoot oil. The process of 
rendering consists essentially in the separation of the fatty 
matter from the enclosing animal tissue. Tallow was originally 
obtained by boiling the finely divided parts of the animal 
containing the fat in water and skimming from the surface 
of the water the fat thus disengaged from the membrane. 
Fleshy portions of the animal previously finely chopped and 
rendered in the manner just mentioned yield the kettle- 
rendered tallow used for edible purposes. Tallow, not of 
packing-house origin, is usually distinguished as country or 
city rendered. 



MANUFACTURE OF SOAP, PART 1 


7 



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OQOOQOOQO o o OOQO 0 008 
OOOOOOOOOOO OOOOOOft- 




10. Steam Rendering-.—St earn-rendered tallow is 
obtained by subjecting the rough fat to a steam pressure of 
30 to 60 pounds per square inch in a closed vessel, such as is 
shown in Fig. 1. The top of the tank is on the floor level 
and is provided with a safety valve, a 
manhole a for introducing the rough 
fat, which is commonly conveyed in 
barrows, and a discharge pipe for the 
exit of fumes. Near the middle of 
the tank are two draw-off cocks (not 
shown in the figure) for the removal 
of the liquid tallow. Water is ad¬ 
mitted through a valve near the bot¬ 
tom. At the bottom of the tank is 
either a large gate valve b or a tightly 
fitting door for the discharge of the 
“soup.” The soup, or soup liquor, as 
it is called in the packing house, con¬ 
sists of soft bones, solid residuum, and 
water highly impregnated with al¬ 
buminous matter. The liquid portion 
is run off and evaporated to a sirupy 
consistency under a partial vacuum, 
and is afterwards mixed with the solid 
matter freed from an excess of liquor 
by compression in a fertilizer press. 

This material constitutes the tankage 
fertilizer of the packing house. 

After charging, these tanks, which 
are usually arranged in a series, are 
tightly closed. Water is run in, if de¬ 
sired, and steam is turned on. The 
period of working varies from 4 to 
10 hours, according to the size of the tanks, the quantity of 
material introduced, and the steam pressure. At the expira¬ 
tion of the rendering period, the fat is discharged by means of 
the draw-off cocks. When the last portions of fat are below 
the level of the draw-off cocks, water is admitted into the tank 






o° 

..0000 90 o o o„o 0„0 O O O O (jo 
OOOQOOOQQ O O Q ° O O O O O Q 


wwftfmss: 





Fig. 1 









































8 


MANUFACTURE OF SOAP, PART 1 


from below, and the fat floating on the surface of the water is 
thus completely discharged. The remaining contents of the 
tank is then dropped through the discharge gate at the bottom. 

11. Chemical Rendering. —While most of the animal 
stock used in the manufacture of soap is prepared by the steam¬ 
rendering process, chemical rendering is carried on to a 
considerable extent. For this purpose, dilute liquors of 
either sulphuric acid or caustic soda are used, and the odorous 
substances present in the stock become partly destroyed or 
combined with the chemical agent used. If the acid process 
is employed, wooden or lead-lined tanks must be used for the 
operation. 


VEGETABLE SOAP STOCK 

12. Any vegetable oil may be employed for the manu¬ 
facture of soap, its applicability for this purpose being deter¬ 
mined by its character, cost, and the intended use of the soap 
made from it. Except in making soft soap or soap for 
special purposes vegetable oil is seldom used alone. How¬ 
ever, oil of some character finds its way into most every 
soap charge. Linseed oil and the various nut oils—peanut oil, 
for example—cannot compete with cottonseed oil because of 
their greater initial cost, although in cases of very large flax 
crops linseed oil has been cheaper than either cottonseed or 
corn oil. Castor oil is used but little, its very limited con¬ 
sumption being confined to the manufacture of transparent 
soaps. Linseed oil is used extensively in Europe in the manu¬ 
facture of soft soap. In the United States soft soap finds 
only limited sale as a detergent. The soft soaps used in the 
cotton and woolen industries are made from a non-drying 
glyceride base. In Table I is given the average percentage 
yield of oils of vegetable origin. The percentage yield of 
oil from seeds, fruits, etc. is dependent on a variety of con¬ 
ditions, chief among which are the character of the soil, the 
weather, and the degree of ripeness, and these are subject to 
extreme variations. These conditions influence, as well, the 
specific gravity of one and the same oil. Moreover, according 



MANUFACTURE OF SOAP, PART 1 


9 


to the age, mode of preparation, etc., of the oil, the varia¬ 
tions in specific gravity may be as great as the difference 
between the density of one oil and that of another serving as 
an adulterant. 

13. Cottonseed Oil. —The chief product of cottonseed, 
which constitutes about two-thirds of the weight of the 
unginned cotton grown in the Southern States, is cottonseed 
oil. In recent years, this oil has attained great importance 
as a soap stock, although its use in this connection is small 
compared with its consumption for edible purposes. Crude 
cottonseed oil is a thick, reddish-brown to black oil of extremely 

TABLE I 


YIELD OF OIL FROM VARIOUS SEEDS, NUTS, ETC. 


Seed 

Percentage 
Yield of Oil 

Seed 

Percentage 
Yield of Oil 

Castor (Indian) . . 

51-53 

Maize, or corn .. . 

6-10 

Castor (American) 

46-49 

Olive (pericarp) . . 

40-60 

Coconut . 

40-45 

Palm (pericarp) . . 

65-72 

Colza, or rape .... 

33-43 

Palm kernel. 

45-50 

Cottonseed. 

24-26 

38-40 

Peanut . 

43-45 

50-57 

Linseed. 

Sesame. 




varying quality, depending on the season and the care exer¬ 
cised in the collection and storage of the seed. The crude oil 
contains from 10 to 15 pounds of coloring matter per ton of 
seed. This coloring matter has been isolated, but is of little 
practical value. The loss in refining the crude oil is from 
5 to 7 per cent. This is an extremely varying factor, depend¬ 
ing on the percentage of free fatty acids and the proportion 
of coloring and albuminous matter present, or, briefly, on the 
character of the seed. The yield of oil depends on the soil, 
season, and skill of manufacture, and ranges from 35 to 42 
gallons of crude oil per ton of seed. 

14. Refining of Crude Cottonseed Oil. —In the refin¬ 
ing process, the first step is to separate as quickly and as 























10 


MANUFACTURE OF SOAP, PART 1 


thoroughly as possible the foreign matter from the expressed 
crude oil. The residue obtained on settling or filtration is 
known as settlings or foots. The precipitate, or residue 
obtained in the refining process is sometimes termed soap 
stock but is known in the cottonseed trade as cottonseed foots , 
under which name it is sold. (Foots is a loose term at best, 
and foots and soap stock are frequently used indiscriminately.) 
The crude oil freed from settlings is now pumped into the 
first-treatment tank, where it is agitated under increased 
temperature with caustic-soda lye of strength and proportion 
adapted to the quality of oil undergoing treatment. When 
sufficient time has elapsed for the complete absorption of the 
alkali, the agitation is ceased and the contents of the kettle is 
allowed to remain at rest. During this time the soap, which 
is formed by the combination of the free fatty acids with the 
caustic alkali and is contaminated with the organic impurities 
of the oil, settles to the bottom. The supernatant oil thus 
partly clarified is then transferred to the second-treatment 
tank, where it undergoes a bleaching process with fullers’ 
earth. The proportion of fullers’ earth used varies with the 
quality of the oil and may run from 2 to 5 per cent.; often a 
second treatment with fullers’ earth after filtration is required. 

The oil after agitation with fullers’ earth, under increased 
temperature, is passed through the filter press. The filtrate 
constitutes the prime summer yellow cottonseed oil used in 
soap making. The various grades of edible and industrial 
cottonseed oils are obtained from this product by subsequent 
treatments with fullers’ earth and filtration. The winter 
cottonseed oil used in miners’ lamps requires limpidity 
at a low temperature. This condition is obtained by chilling 
the oil to a temperature below 0° C., whereby the so-called 
cottonseed-oil stearin , which is really palmitin, separates. 
This cottonseed stearin is used in the manufacture of oleo¬ 
margarine, and of butter and lard substitutes. 

15. Grades of Cottonseed Oil. —The requirements of 
the Texas Cottonseed Crushers’ Association for the various 
grades of cottonseed oil compel a uniformity of quality that 


MANUFACTURE OF SOAP, PART 1 


11 


is absent in the soap stock of animal origin. The summer 
yellow oil employed in soap manufacture is usually examined 
for color, moisture, free fatty acids, and titer, the last test 
being of chief importance in determining comparative value 
for the use of soap makers. 

16. Crude Cottonseed Oil. —The following are rules 
of the Texas Cottonseed Crushers’ Association relating to 
cottonseed oil: 

Measurement. —A tank (tank car) of cottonseed oil shall be 125 barrels. 
A barrel of oil, if sold loose, shall contain 50 gallons. A gallon of oil 
shall weigh 7\ pounds, avoirdupois. 

Classification. —Crude cottonseed oil shall be classed and graded as 
follows: 

Choice crude must be made from sound decorticated seed, must be 
sweet in flavor and odor, light in color, free from water and settlings, 
and test not over 1 per cent, of free fatty acids. It shall produce, when 
properly refined, choice summer yellow oil at a loss in weight not exceed¬ 
ing 6 per cent, for Texas oil, and at a normal loss for oil from all other parts 
of the country. 

Prime Crude. —Crude cottonseed oil to pass as prime must be made 
from sound decorticated seed, must be sweet in flavor and odor, free from 
water and settlings, and must produce prime summer yellow grade by 
the usual refining methods with a normal loss in weight, provided the 
oil shall not be rejected for a nominal amount of settlings; but reasonable 
reduction shall be made in value for all such settlings in excess of ^ per cent. 

Off Oil. —All oil neither choice nor prime shall be called off oil, and 
shall be sold by sample. 

17. Refined Cottonseed Oil. —According to the rules 
of this association, refined cottonseed oil shall be classed and 
graded as follows, summer yellow oil only being considered: 

Choice summer yellow must be sweet in flavor and odor, of light straw 
color, clear and brilliant in appearance, free from moisture, and must bleach 
to a choice white. 

Prime summer yellow must be clear, sweet in flavor and odor, and of 
yellow color, not reddish, and free from water and settlings. 

Off Oil. —This grade consists of all oils having any objectionable flavor 
or odor, or that are of a reddish color. 

18. Cottonseed Oil Soap Stock. —The precipitate 
obtained from the crude oil freed from settlings, on treatment 
with caustic-soda lye, consists of soap and free oil mixed 
with mucilaginous and coloring matters. This mixing 


12 


MANUFACTURE OF SOAP, PART 1 


undergoes further treatment with caustic alkali, which trans¬ 
forms all the free oil into soap. The finished soap is grained, 
and is then subjected to further brine and alkali washings in 
order to obtain a product as free from odor and light in color as 
possible. After this stock has been suitably purified and is 
on the final settling, it is run while hot and in a semifluid 
condition into barrels. 

19. Requirements of the Texas Cottonseed 
Crushers’ Association for Soap Stock. —According to 
the requirements of the Texas Cottonseed Crushers’ Associ¬ 
ation, all sales, unless otherwise agreed on by buyer and 
seller, are on a basis of 50 per cent, of fatty acid, not to fall 
below 40 per cent. If containing less than 40 per cent, of 
fatty acid, soap stock shall not be considered merchantable. 
Delivery is to be made in iron-bound hardwood packages or 
tank cars. A tank car of soap stock shall be 50,000 pounds 
for contract purposes. 

20. Coconut Oil. —The fruit of the coco palm, the Cocos 
nucifera of the tropics, is the source of coconut oil. The 
oil is expressed from the pulp of the nut, which contains about 
50 per cent, of oil. It occurs on the market in three general 
grades, namely, Cochin, Ceylon, and copra oil. The terms 
Cochin and Ceylon have reference to the geographical origin of 
the fruit. 

Considerable coconut oil is produced in the West Indies 
and in the tropical parts of America. That from Trinidad 
compares very favorably in color, body, and odor with the 
Cochin grade; but that from Cuba is inferior in quality and 
yellowish in color, and therefore cannot be used for the better 
grades of bath and floating soaps. Cochin coconut oil is 
usually sufficiently superior in quality to command a price of 
from | to 1 cent a pound more than Ceylon oil. 

Cochin coconut oil is expressed from fruit grown in Cochin- 
China and adjacent territory, and on the islands of the 
China Sea. 

Malabar and Manila oil is of good quality. Mauritius and 
the Fiji Islands also produce considerable. The coco palm is 


MANUFACTURE OF SOAP, PART 1 


13 


a native of Cuba, and at one time oil crushing was a thriving 
industry on that island. 

Ceylon coconut oil is a product of the island of Ceylon and 
of the adjacent regions. The different grades of coconut oil 
arise from the varying skill and the nature of the apparatus 
employed in its recovery, some of the apparatus being very 
crude. Where improved milling machinery has been intro¬ 
duced, coconut oil of uniform and superior quality is obtained; 
the greater part of the oil, however, is extracted by the most 
primitive methods. The oil arrives at the factory in immense 
casks, pipes, puncheons, and hogsheads containing from 800 
to 2,000 pounds. 

Copra coconut oil is made from the dried pulp or meat of 
the coconut, called copra. This pulp yields, on steaming and 
pressing, the lowest grade of coconut oil. The best oil of 
this grade is obtained from the ripest and most quickly 
pressed copra. Owing to its high percentage of the lower 
fatty acids and to its greater exposure, the copra oil is more 
liable to become rancid than is oil of the Ceylon and Cochin 
grades. The Ceylon and Cochin oils are expressed in the 
districts near the shipping ports, while copra is produced almost 
entirely in territory deficient in shipping facilities. Great 
quantities of copra are shipped to Marseilles, France, where 
the oil is expressed. In Sydney, New South Wales, copra 
crushing is a thriving industry. 

21. Coconut oil is desirable as a soap stock because it 
contains a high glycerine yield and possesses distinct and 
peculiar qualities that define it sharply from all other animal 
and vegetable oils. In this connection, it may be well to 
note that there is no sharp distinction between a fat and an 
oil. Fat, which is usually of animal origin, is the term 
generally applied to the glycerides that are solid at ordinary 
temperatures; oil, on the other hand, may be of either animal 
or vegetable origin and is liquid at ordinary temperatures. 

22. Palm-Kernel Oil. —In its chemical composition 
and behavior toward saponifying agents, palm-kernel oil is 
closely allied to coconut oil. While it is used extensively in 

394—2 




14 


MANUFACTURE OF SOAP, PART 1 


Europe, it finds only limited application in the United States 
as a soap stock. It is expressed from the kernel of the 
palm nut, the fleshy envelope of which is the source of palm 
oil. The oil is white and has an agreeable odor and taste, 
but on aging it becomes rancid. Oudemans gives the follow¬ 
ing as the approximate composition: 


Clyceride 
Olein 
Stearin 
Palmitin ► 
Myristin J 
Laurin 
Caprin 
Caprylin 
Caproin 


Per Cent. 
. .26.6 

. . .33.0 


44.4 


23. Palm Oil. —The fleshy part of the fruit of the palm 
tree, the Elais Guineensis and the Elceis melanococca, native 
along the west coast of Africa, is the source of palm oil. 
According to its source and the mode of expressing it, palm 
oil is of butter-like to tallowy consistency, varying in color 
from orange to dark red, and possesses a characteristic violet¬ 
like odor. 

The oil can be bleached by blowing air through it for a 
number of hours while the oil is maintained at a temperature 
of 80° to 90° C. But this can be accomplished better and 
more quickly by chemical bleaching, which destroys the odor 
as well as the color. 

The chemical bleaching of palm oil is carried out in the 
following manner: After carefully removing all water and 
impurities by subsidence, the oil, cooled to a temperature of 
105° to 110° F., is pumped into a lead-lined tank. While 
being constantly agitated by air, J of 1 per cent, of bichro¬ 
mate of soda dissolved in the least possible amount of water 
is run in, followed by per cent, of hydrochloric acid and 
\ per cent, of sulphuric acid. At the end of 20 minutes the 
bleaching will be finished, and the acids and oxide of chromium 
are removed by allowing 25 per cent, of hot water to run 








MANUFACTURE OF SOAP, PART 1 


15 


in. It is preferable to allow the contents of the tank to remain 
undisturbed over night and to remove the clear oil in the 
morning. 

The Lagos oil is the best quality made; it is of a deep, 
reddish-orange color and contains free fatty acids averaging 
from 20 to 30 per cent. The common grades of palm oil 
are yellow in color, and on account of the primitive methods 
employed in extracting them, the free fatty acids are very 
high, running from 50 to 80 per cent. Deductions for mois¬ 
ture, dirt, and impurities are allowed on sales made, provided 
they amount to over 2 per cent., which is generally the case. 

Since the titer of palm oil is very uniform, never varying 
much from 44° to 45° C., the chief industrial chemical tests 
made are the determinations of the impurities and of the 
free fatty acids present. 

24. Corn Oil. —The germ obtained as a by-product in 
the manufacture of starch and glucose from maize is utilized 
in expressing corn oil. This oil is closely allied to cotton¬ 
seed oil in its soap-making properties. It is usually of a 
bright-yellow color, but may be bleached with fullers’ earth 
to whiteness, as is done with certain edible grades of cotton¬ 
seed oil. 

In the manufacture of the oil, the corn is first steeped in 
water, so as to loosen the hull from the grain, which becomes 
swollen and tough from the absorption of water. The 
steeped kernel is then passed between rollers to separate 
the envelope and the starch from the softened germ, which 
remains whole and of the size of a grain of rice. The crushed 
corn is then transferred to tanks filled with water, in which 
the crushed grains sink, leaving the germs to float on the sur¬ 
face. These are removed, cooked, and compressed for the oil. 

On account of its higher titer, from 33° to 35° C., cotton¬ 
seed oil as a soap stock is much to be preferred to corn oil, 
the titer of whose fatty acids ranges from 17° to 19° C. Corn 
oil mixed with other stocks is used quite extensively in the 
production of soaps of soft body, to be used in the manu¬ 
facture of soap powders. This mixture gives a soap readily 


16 


MANUFACTURE OF SOAP, PART 1 


soluble in cold or lukewarm water, a characteristic very 
essential to a good powder. 

25. Olive Oil. —The pulp, or fleshy portion, of the fruit of 
the oilve tree, the Olea Europcea, native in the Mediterranean 
countries, is used for making olive oil. In these countries, 
olive oil has been employed from the earliest time as the fatty 
base of Castile soap. The use of olive oil for this purpose 
has of late years been largely displaced by the cheaper cotton¬ 
seed oil, large quantities of the latter being exported from 
the United States to Marseilles for this purpose. Olive 
oil is used chiefly as an edible oil, and inferior grades only 
are used in the soap kettle. Olive oil finds very limited use 
as a soap stock in the United States. It contains about 72 
per cent, of olein and 28 per cent, of palmitin, and behaves 
like cottonseed oil toward saponifying agents. 

In the manufacture of olive oil, about 10 bushels of olives 
is crushed at a time in an edge-stone mill. The pasty mass 
that results, consisting of pulp and stones, is then placed in 
filter cloths and subjected to hydraulic pressure. The first 
pressing of the olives yields the finest oil. After the first 
pressing, which yields the virgin oil, as it is sometimes called, 
the press cake is ground up with water in the edge-stone mill, 
and the paste is then subjected to a second pressing. The 
second pressing yields an oil of inferior quality. The press 
cake after the second pressing still contains a large quantity 
of oil which, when recovered, constitutes the olive-oil foots of 
commerce. Table II shows the specific gravity, weight per 
gallon, etc. of the principal fatty oils. 

26. Olive-Oil Foots. —The oil remaining in the press 
cake after the second pressing may be extracted in either of 
two ways, but when recovered it is of such inferior quality 
as to be suitable only for industrial purposes. It is fairly 
fluid, dark green to black in color, and has a disagreeable 
odor. Its inferiority results from being contaminated by the 
green coloring matter and pulp of the fruit. To recover the 
remaining oil, the press cake is first well ground, hot water 
being added during the process. The dark pasty mass is 


MANUFACTURE OF SOAP, PART 1 


17 


then transferred to a tank and agitated with water until the 
broken olive stones drop, free from pulp, to the bottom of the 
tank. The oily residuum floating on the surface of the water is 
then transferred to another tank, where the free oil is removed. 
The pulp residuum is 'again pressed and yields some oil. 
Olive-oil foots obtained in this manner are said to be washed. 

The press cake may also be extracted with a volatile 
solvent, carbon disulphide or naptha being commonly used. 

TABLE II 

SPECIFIC GRAVITY OF FATTY OILS AT 15° C. (60° F.) 


Name of Oil 


Specific Gravity 


Almond oil. 

Arachic (peanut) oil 

Castor oil. 

Coconut oil. 

Corn oil. 

Cottonseed oil. 

Lard oil. 

Linseed oil . 

Neatsfoot oil .. 

Olive oil . 

Palm oil . 

Palm-kernel oil .. .. 

Rape oil . 

Sesame oil. 

Tallow oil. 

Tallow. 


.918-919 

.917—920 

• 959-967 

.924-926 

.921-922 

• 923 - 9 2 5 
.912-915 
.932-936 
.914-917 
.916-.918 

• 943-946 
.9119 (at4o°C.) 
.913-917 
. 924-926 
.910-.912 
.943-952 


The broken press cake is agitated with the solvent, after 
which the solution thus obtained is transferred to a covered 
tank. Here the solvent is distilled off and collected for 
subsequent use, leaving the recovered oil behind. This oil 
is black and retains the odor characteristic of the solvent. It 
is inferior to washed foots. This process, however, possesses 
the advantage of extracting the oil completely. 





























18 


MANUFACTURE OF SOAP, PART 1 


Soap made from olive-oil foots retains the green color of 
the recovered oil; the color, however, gradually bleaches out 
on exposure. 

27. Red Oil. —In the manufacture of candles, a by¬ 
product known as red oil is obtained. This oil consists 
almost wholly of oleic acid, and derives its name from the color 
that it acquires on aging. The color, however, is chiefly 
due to contact with the iron. Sometimes this color is 
developed by the use of dyes and sometimes by chemical 
treatment with sulphur or nitric oxide. Red oil occurs in two 
grades, namely, saponified and distilled red oil. 

Saponified red oil is obtained by either acid, lime, or 
aqueous saponification under pressure, in specially con¬ 
structed tanks called autoclaves, or digesters. The mixed 
fatty acids resulting from saponification are resolved roughly 
into stearic and oleic acids by pressure through filter cloths. 
The stearic acid still remaining in the liquid portion is sepa¬ 
rated by chilling, whereby the commercial oleic acid, or red 
oil, is obtained. 

Distilled red oil is obtained by distilling the mixed fatty 
acids with steam. By means of the process of fractional 
condensation, fatty acids of different melting points are 
separated. Distilled red oil varies in its composition accord¬ 
ing to the method employed in its manufacture. The follow¬ 
ing are analyses of two samples of commercial oleic acid: 


Ingredients 

Sample A 
Per Cent. 

Sample B 
Per Cent. 

Color . 


Brown 

Oleic acid. 

. 93.06 

87.70 

Oil. 

. 6.04 

9.41 

Hydrocarbons. 

. 90 

2.89 

Total . 

.100.00 

100.00 

Specific gravity. 

. 897 

.904 

Turbid at. 

. 42 ° F. 

38 ° F. 


Red oil is a valuable soap stock. It admits of a nearly 
complete saponification with soda ash, as will be fully explained 
elsewhere. 











MANUFACTURE OF SOAP, PART 1 


19 


28. Manufacture of Saponified Red Oil. —Saponified 
red oil, as just stated, may be obtained by three methods of 
saponification, namely: lime saponification, acid saponifica¬ 
tion, and aqueous saponification. 

29. Lime-Saponification Process. —The digester, or 
autoclave, used in the lime-saponification process, is a strongly 
built tank, usually of copper, although some are made of iron, 
from 3 to 5 feet in diameter and from 18 to 25 feet in height. 
The digester may be set up either horizontally or vertically. 
It is covered with an asbestos jacket, to retain the heat, and 
is provided with a safety valve, a cock for the removal of 
samples, and a pressure gauge. At one end are located pipes 
for the introduction of the tallow and lime, for the discharge 
of the contents of the digester after saponification, and for 
the introduction of live steam. 

The tallow is previously purified, if required, by boiling in 
weak brine and then allowing the impurities to subside. The 
brine wash is then run off, and the tallow is maintained in a 
fluid state by means of a closed steam coil. The quantity of 
unslaked lime commonly used for saponification is from 2 to 
4 per cent, of the weight of the tallow. Both the tallow and 
lime tanks are on an elevation above the digester, and after 
the lime has been thoroughly mixed with water and the 
tallow melted, they are allowed to run by gravity into the 
digester. The charging of the digester may be hastened by 
creating a partial vacuum in it by the condensation of steam 
previous to running in the charge. 

After the charge has been added, steam is turned on and 
maintained at a pressure of from 8 to 10 atmospheres for a 
period of from 4 to 10 hours, or until the saponification is 
complete; 8.7 per cent, of lime is theoretically required, but 
under the conditions maintained in the digester, from 2 to 4 per 
cent, has been found to be sufficient in practice. Samples 
are removed from time to time and tested for unsaponified 
matter. On completion of saponification, the contents of the 
disgester is blown into wooden tanks, or vats, situated above 
the digester. 


20 


MANUFACTURE OF SOAP, PART 1 


The mass resolves itself into two layers: the supernatant 
lime rock , consisting of lime soap and fatty acids, and the sweet 
water, in which is dissolved the glycerine liberated from the 
stock. The glycerine solution is now allowed to flow by 
gravity to the glycerine plant, while the lime rock is again 
boiled up with water and live steam in order to remove the last 
traces of glycerine. This wash liquor is removed as before. 

The decomposition of the lime rock is effected by adding 
slowly, under constant agitation, the calculated quantity of 
dilute sulphuric acid. The fatty acids of the lime soap are 
thus set free. The mass at once resolves itself into two 
layers: the supernatant layer, consisting of the total fatty 
acids, and the water containing the calcium sulphate in solu¬ 
tion and as a precipitate. The acid liquor and precipitate 
are now discharged into the sewer, and the fatty acids are 
washed free from all traces of sulphuric acid. 

30. Acid-Saponification Process. —In Fig. 2 is shown 
a type of apparatus of English manufacture employed in the 
acid-saponification process for the manufacture of fatty acids 
for candle stock. 

The raw material, whether it be tallow, palm oil, recovered 
grease, or any fatty body containing stearin, is first melted 
in the tank marked A and is then transferred to the storage 
tanks G. These tanks are wooden and lead-lined and are 
provided with acid-resisting steam coils. In these storage 
tanks the fat undergoes a preliminary purification, as already 
briefly described. The mass is then transferred to the acidifier 
marked D. It is there treated with from 4 to 12 per cent, of 
concentrated sulphuric acid, which is introduced by gravity 
from a tankE located immediately above. In the acidifier D, 
the mixture is subjected to the action of superheated steam 
furnished by the superheater F. To condense the acrid 
vapors evolved during the reaction, a jet condenser provides 
a slight vacuum in the acidifier, and the vapors are thus drawn 
over and discharged into the reservoir d. 

After the acidification is complete, the material is dis¬ 
charged into the storage tanks U, where the acid liquor is 




21 



Fig. 






























































































































































































































































































































































22 


MANUFACTURE OF SOAP, PART 1 


removed and the fatty acids are washed free from all traces 
of sulphuric acid. 

31 . Aqueous-Saponification Process. —Many estab¬ 

lishments manufacturing candle stock employ neither acid 
nor lime in the hydrolysis of the glyceride, but saponify 
their tallow, bone fat, or other stock merely in the presence 
of water and a catalyst under a steam pressure of 150 pounds. 
These catalysts, or saponifiers, are usually made by the action 
of sulphuric acid on a solution of oleic acid in an aromatic 
hydrocarbon. This hydrocarbon may be benzene, toluol, or 
naphthalene. Higher alcohols have also been successfully 
employed, such as phenol and cetyl alcohol. It can readily 
be seen how a sulphonated product is obtained which in 
the case of benzene corresponds to It 

requires from 1 to 2 \ per cent, of the saponifier for the reaction, 
which proceeds best when the fat or oil contains a little free 
fatty acid of its own. This is called the autoclave process. 
Saponification by means of water is the simplest and most 
convenient of the three processes described, inasmuch as the 
lime and acid treatments are made unnecessary. The process 
otherwise is carried on in precisely the same manner as 
described in the lime-saponification method. 

32 . Twitcliell Process. —A process for the separation of 
the fats and oils into fatty acid and glycerine has been worked 
out by Twitched. This process differs from similar processes 
in that he employs a saponifier. This saponifier is made by 
allowing sulphuric acid to act on oleic acid in the pressure of 
an aromatic hydrocarbon, benzene or naphthalene. When 
benzene is used the formula for the saponifier may be 
expressed as CeHfiS0 3 H)Ci 8 H3 b 02. 

The process requires that the original fat or oil be purified 
by boiling with dilute sulphuric acid. It is then mixed with 
an equal amount of distilled water and lj to 2 per cent, 
of the saponifiers and boiled in wooden tanks, fitted with 
brass coils and a tight cover. Any access of air tends to 
darken the fatty acid and this has been one of its chief 
drawbacks. 


MANUFACTURE OF SOAP, PART 1 


23 


The Twitchell product often has to be distilled to get light- 
colored fatty acids. It has not found great favor with the 
soapmakers as yet. 

33 . Distillation of the Fatty Acids. —The fatty acids, 
whether obtained by the lime, acid, or aqueous saponifica¬ 
tion, are subjected to the same process of distillation. When 
made of pure and fresh raw material, the resulting fatty 
acids are of sufficiently good color to press immediately. 
The dark-colored fatty acids before pressing are subjected 
to distillation with superheated steam. Referring to Fig. 2 , 
the fatty acids are pumped to the charging tank H situated 
on an elevation above the still I, into which these acids may 
flow by gravity. The still, generally of copper or copper- 
lined, is of variable capacity. A still of ordinary size will 
accommodate from 16,000 to 18,000 pounds at a run , during 
which the volume of material in the still is kept constant by 
the addition of fatty acids from the charging tank above. 
As shown in Fig. 2 , the still is incased in brickwork and is 
heated externally by fire and within by superheated steam, 
which passes through copper coils from the superheater F. 
The products of distillation are condensed in the vertical 
cooling tubes k , which connect at the bottom with coils 
immersed in warm water. The condensed fatty acids are 
here melted, to admit of their easy removal. The distillate 
is commonly collected in three fractions, namely, the first- 
run oil, comprising three-fourths of the total charge; the 
second-run oil, which is returned to the charging tank and 
redistilled with the next run; and the final portion, called from 
its color green oil. The residue in the still is known as candle 
tar. 

34 . Pressing the Fatty Acids. —The fatty acids, 
whether having been subjected to a previous distillation or 
used directly from the autoclave, are transferred to square, 
shallow pans, or trays, supported on shelves in the granulating 
room. These trays are of enameled iron and are so placed 
that each tray, beginning at the end, is at a higher elevation 
and slightly over the succeeding one. It is thus possible to 


24 


MANUFACTURE OF SOAP, PART 1 


fill every pan in the series by running the melted fatty acids 
into the topmost, which, when full, overflows into the succeed¬ 
ing one, and so on until all are filled. Were the fatty acids 
cooled rapidly, the crystals of the fatty acids of different 
melting points would be so closely interlocked that the oleic 
acid could not be readily separated from the stearic. By 
allowing the mixture of fatty acids to cool slowly for a period 
of frcm 2 to 3 days in the granulating room, at a temperature 
of about 80 ° F., the stearic acid crystallizes in a menstruum of 
the liquid oleic acid. There is thus obtained at the expiration 
of this stage of the process a cake of stearic acid colored brown 
by the oleic acid. 

The pan is now inverted on a woolen or a cameFs-hair 
cloth, on which the cake falls. When the required number 
of cloths have been filled they are transferred to the hydraulic 
press. Each cloth with its contents is separated by an iron 
plate. Pressure is applied very gradually at first, whereupon 
the crude oleic acid, or red oil, is expressed. The oil is then 
conducted to storage tanks, from which it either is run to the 
department in which it is used or is barreled for shipment. 

The first pressing separates about 50 per cent, of the oleic 
acid present and is done cold. The cakes thus obtained are 
subjected to a second pressing between hollow iron plates 
heated with steam. The hot pressing is effected in a hori¬ 
zontal hydraulic press. The stearic acid now obtained is of 
snowy-white appearance and very hard and brittle. It melts 
at 52 ° to 55 ° C. and is ready for the candle manufacturer. 

35 . Comparison of the Processes for the Manufac¬ 
ture of Fatty Acids. —The yield of solid fatty acids from 
tallow by lime saponification is from 44 to 48 per cent. Aque¬ 
ous saponification admits of a slightly higher yield, namely, 
50 per cent., from the same raw material; acid saponification 
yields upwards of 55 per cent, of fatty acids. It is found in 
practice that distilled stock yields a press cake of lower 
melting point than that obtained from fatty acids used directly 
from the autoclave. This fact taken together vith the 
greater yield of the acid-saponification process with which 


MANUFACTURE OF SOAP, PART 1 


25 


process distillation is used may be explained by the poly¬ 
merizing action of the sulphuric acid on the oleic acid in the 
still, whereby a body is formed of sufficient firmness to resist 
being expelled from the press cake with the crude oleic acid, 
and thus remains to lower the melting point and to add to the 
yield. 

With lime saponification, practically all the glycerine, 
upwards to 10 per cent., is obtained; with the acid saponifica¬ 
tion, not more than 3 per cent, is recovered. If it is desired 
to recover as much glycerine as is possible, in addition to the 
solid fatty acids, the lime saponification is preferable. If 
fatty acids are the sole desideratum, the distillation process is 
better. 


36 . Rosin. —The solid residue left on the distillation of 
crude turpentine is rosin. The rosin, or crude turpentine, 
exudes from the pine 
tree, chiefly the long- 
leaf yellow pine of the 
Southeastern Atlantic 
and Gulf States. This 
rosin is of whitish color 
and of semisolid con¬ 
sistency. A number 
of deep incisions are 
made in the trunk of 
the tree starting about 
1 foot from the ground, and each incision, or box holds about 
a quart of the crude rosin. The number of boxes cut in each 
tree, depends on the size of the tree. As the season advances, 
the flow of rosin is increased by removing the bark and wood 
to the depth of 1 inch above the box. At regular intervals, 
the exuded rosin is collected and distilled. 

The still (see Fig. 3 ) used for distilling rosin is made of 
copper and varies in capacity from 10 to 50 barrels of crude 
turpentine. It is mounted on brickwork and has a furnace 
underneath. After the still has been charged, some water 
is run in and the contents is heated. The fire is increased 











26 


MANUFACTURE OF SOAP, PART 1 


gradually until the contents of the still has reached the boil¬ 
ing point, which temperature is maintained until practically 
all the volatile matter has been distilled over. As the dis¬ 
tillation proceeds, water is added from time to time so as to 
replace that lost by evaporation and to prevent the product 
from being darkened by incipient burning. The distillate, 
separated from the water that has distilled over with it, 
constitutes the oil of turpentine of commerce. The hot 
liquid residuum in the still is now discharged through a valve 
near the bottom, strained through sieves of increasing mesh 
up to No. 80, usually three in number, and is finally run into 
barrels. A charge of 12 barrels of crude turpentine, weighing 
upwards of 4,500 pounds, will yield on distillation about 3,600 
pounds of rosin and about 900 pounds of oil of turpentine. 

37. The gross weight of a barrel of rosin is about 500 
pounds and the net weight averages 420 pounds, the barrel 
itself always being paid for at the same rate as the rosin. 
Rosin is marketed on a basis of 280 pounds to a barrel, and 
according to law, the empty barrel may weigh 15 per cent, 
of the weight of the barrel when filled. This is equivalent to 
40 pounds for Alabama and 70 pounds for Savannah cooperage. 

Opaque rosins contain turpentine and water, and when 
used in soaps they affect the hardness to a certain extent; 
that is, the soaps become soft in very hot weather. 

There are about fifteen grades of rosin, varying in color 
from water white , which is clear and almost colorless, to the 
lowest grade, commercially known as “C. A.,” which is 
black. The various qualities arise from the length of time 
during which the crude rosin is collected from a single camp. 

The first year’s run furnishes the best grades, while with 
each succeeding year a more inferior grade is obtained. The 
following grades are used in the soap industry: 

W. W., or Water White. 

W. G., or Window Glass 
N., or Extra Pale 
M., or Pale. 

K., or Low Pale. 


MANUFACTURE OF SOAP, PART 1 27 

Most of the rosin used for soap making is of the M and N 
grades. 

Rosin is graded by sample, a J-inch cube being cut from 
the head of each barrel. Uniformity of size is important, as 
the thickness of the cube determines the shade of color, and 
therefore the value. Those who buy and sell rosin are pro¬ 
vided with sample cubes representing the quality of the 
standard grades. The determination of the quality of a ship¬ 
ment, therefore, is simply a matter of comparing the sample 
cubes with those of the standard grades. 

38. Rosin is acid in its composition, consisting of the 
anhydrides of the so-called rosin acids. Like red oil, rosin 
can be almost entirely saponified with soda ash. The alka¬ 
line salts of the rosin acids, while not constituting a true 
soap, possess marked detergent properties and are a valuable 
ingredient of household soap. The English were the first 
manufacturers of rosined soaps. 

As rosin decreases in quality from the brighter to the 
darker grades, the percentage of unsaponifiable matter 
increases, as is indicated by the following determinations of 
the unsaponifiable matter: 


Percentage 

Marks Unsaponifiable 

Matter 

W. W.3.07 

W. G.3.88 

N.4.08 

M.6.34 

K.6.62 


The coloring matter present in rosin is the cause of the 
high color of the waste soap lye withdrawn after the rosin 
change in the manufacture of settled rosin soap. 







28 


MANUFACTURE OF SOAP, PART 1 


ALKALIES AND THEIR MANUFACTURE 

39. Soda Ash, or Sodium Carbonate. —All the com¬ 
mercial sodium compounds start from common salt as a raw 
material. Before the development of the Le Blanc process, 
potash was used exclusively as the saponifying agent in the 
primitive soap manufacture of those days. The potash was 
obtained by burning sea-weeds and lixiviating the ashes. The 
solution thus obtained was then causticized with quicklime. 
During the embargoes of the French Revolution, the supply of 
potash was cut off from France. As the result of a prize 
offered by the French government for a practical method of 
manufacturing soda ash from common salt, the Le Blanc 
process was given to the world. So perfectly was this process 
outlined in its original specifications that it has undergone 
no change in its essential principles in its entire history. 

40. Tlie Le Blanc Process for the Manufacture 
of Sodium Carbonate. —The manufacture of soda ash, 
or sodium carbonate, Na 2 CO s , from common salt by the 
Le Blanc process is carried on practically in three stages, 
as expressed in' the following reactions: 

1. Common salt, or sodium chloride, is converted into 
sodium sulphate by treatment with sulphuric acid. 

2 NaCl + H 2 SO 4 = Na 2 SO*+2 HC l 

The hydrochloric-acid gas is absorbed by passing it through 
towers down which water is allowed to trickle. The aqueous 
solution of the gas thus obtained constitutes the muriatic 
acid of commerce. 

2. The sodium sulphate obtained by the preceding reac¬ 
tion is mixed with coal and fused in specially constructed 
furnaces. The coal reduces the sulphate to sulphide. 

N a 2 S 0\ ~F 2 C — Ncl 2 S -|- 2 C 0 2 

3. The sodium sulphide is now heated with carbonate of 
lime, which then reacts to form calcium sulphide and sodium 
carbonate. 


Na 2 S-\-CaC0 3 ^CaS+NckCOa 


MANUFACTURE OF SOAP, PART 1 


29 


\ 


The product of this reaction is crude soda, or black ash. 
The fused mass is allowed to cool and then broken into 
fragments and lixiviated with water. The sodium carbonate 
in solution is allowed to crystallize out as 10/f 2 O. 

The water of crystallization is expelled by heat, leaving the 
sodium carbonate or soda ash of commerce. 

41 . The Le Blanc process, although a creation of French 
ingenuity, enjoyed its greatest development on English soil, 
and for half a century was one of the chief mainstays of 
England’s industrial supremacy. The practical employment 
of the process involved certain technical and many unsanitary 
disadvantages, whose baneful effects proved a constant 
encouragement for the development of a simpler and more 
hygienic process. The mechanical difficulties surrounding the 
production of alkali by what is now known as the ammonia 
process met their first practical solution at the hands of Ernest 
and Alfred Solvay, and in the past 35 years works operating 
the process originally covered by the Solvay patents have been 
established in every civilized country. The first ammonia- 
soda works were established in Belgium in 1863. Later, 
immense works were established in England by Brunner, 
Mond & Co., whose name is closely associated with the 
development of the process in Great Britain. 

The Le Blanc process has received the most thorough 
scrutiny of the best scientific minds, and the efforts made to 
enable it to survive in the face of the more economical pro¬ 
duction of a competing process have resulted in the most 
complete economy of operation. As a remunerative producer 
of alkali, the ammonia process early displaced it, with the 
result that the process is dependent for its profits entirely on 
its chlorine products. As yet no economical production of 
bleaching powder from the calcium-chloride waste of the 
ammonia-soda process has been wrought out on an extensive 
commercial scale, and as these two rival chemical processes 
stand today, the Le Blanc has command of the chlorine 
industry, while the scepter of remunerative alkali production 
has passed to the ammonia process. 

394—3 


30 


MANUFACTURE OF SOAP, PART 1 


42 . Solvay, or Ammonia-Soda, Process. —The Sol- 
vay process for the production of soda ash from common salt 
is based on the precipitation of sodium bicarbonate in an 
ammoniacal solution of common salt by means of carbonic- 
acid gas. Practically all soda ash now produced is obtained 
by this process. 

In the practical operation of the Solvay process, the employ^ 
ment of labor is reduced to a minimum. The materials 
employed in the direct manufacturing processes are either 
in a gaseous state or in aqueous solution. The fundamental 
chemical reaction of the process is as follows: 

Na Cl + NH z + H 2 0 -f C 0 2 = NH A Cl -f NaHC0 3 

The salt is dissolved in water to form a very pure and con¬ 
centrated brine. It is then saturated with ammonia gas. 
The liquor thus formed is introduced under pressure into the 
carbonating tower at a distance about one-third from the 
top. The carbonating tower is upwards of 65 feet in height 
and is made of up of segments about 3.5 feet high and 6 feet 
in diameter. The carbonic-acid gas is forced into the tower 
through the bottom segment and is made to ascend in bubbles 
by means of a perforated plate covering a hole in the bottom 
of each segment. The reaction indicated by the preceding 
formula takes place in the carbonating tower. The success 
of the ammonia-soda process depends on the insolubility of 
the sodium bicarbonate in a cold, ammoniacal solution of 
common salt. The heat produced by the chemical reaction 
is taken up by cold water circulating in cooling pipes placed 
in each segment of the carbonating tower. 

43 . As the reaction proceeds, the precipitated sodium 
bicarbonate accumulates in the bottom of the tower, from 
which place it is withdrawn from time to time as a thick, 
milky liquid, containing ammonium chloride and sodium 
chloride in solution and the sodium bicarbonate in suspen¬ 
sion. The solid bicarbonate is separated from the chlorides 
of ammonium and sodium in solution by means of centrifugal 
machines, and it is then washed with water to remove traces 
of these impurities. The bicarbonate is then calcined to 


MANUFACTURE OF SOAP, PART 1 31 

form a normal carbonate in accordance with the following 
reaction: 

2 NaHC 0 3 = Na 2 C 0 3 + C0 2 +H 2 0 

The Solvay soda ash thus obtained has a specific gravity 
of only .8, owing to its extremely finely divided condition. 
To increase the ease of handling this soda ash and to bring it 
up to the density of Le Blanc soda ash, namely, 1.2, it is made 
more compact by subjecting it to a second ignition. It is then 
ground and packed in bags and casks for shipment. Soda ash 
made by this process is much purer than the Le Blanc soda 
ash. It contains only traces of salt and bicarbonate and is 
free from the sulphide, sulphate, and hydrate of sodium. 

44. Caustic-Soda Manufacture. —The manufacture of 
caustic soda is based on the following reaction: 

Na 2 C0 3 -\-Ca (OH) 2 = 2Na0H+CaC0 3 
106 74 80 100 

According to this reaction, 100 pounds of sodium carbon¬ 
ate will yield on causticization 75.4 pounds of sodium hydrate. 
In the manufacture of caustic soda from the soda ash of the 
Le Blanc process, the lime is added to the solution obtained 
by lixiviating the black ash. The solution must not have 
a density in excess of 13° Baume, or a reversion of the cal¬ 
cium carbonate will result. The impure solution of sodium 
carbonate is therefore diluted, if necessary, and the milk 
of lime added. Under heating and agitation with air, the 
reaction represented by the preceding formula takes place. 
Zinc oxide is added to reduce the sodium sulphide; thus, 

Na 2 S+ZnO+H 2 0 = 2NaOH+ZnS 
The addition of sodium nitrate, together with the air used 
for agitation, suffices to oxidize any thiosulphate to the 
normal sulphate. The solution is then allowed to settle, and 
the supernatant solution of caustic soda is removed and 
evaporated until a density of 33.5° Baume is attained, at 
which point most salts present as impurities crystallize out. 
The solution is then transferred to a heavy cast-iron pan, 
and the evaporation is continued over fire until all water is 
expelled and the caustic soda remains as a fused mass. 


32 


MANUFACTURE OF SOAP, PART 1 


A sample representing the contents of the kettle is tested 
for total alkali. If found to be below 60 per cent, in quality, 
the contents is worked up to that test. If the test indicates 
the quality to be above 70 per cent., the product may be 
worked into the highest grade or into that grade testing most 
closely to the contents of the kettle. The reduction of quality 
to the grade of caustic desired is effected by the addition of 
salt. The fused caustic soda is then run directly into sheet- 
iron drums and sealed to prevent exposure to the atmosphere. 
Owing to the greater purity of the solutions, purer caustic soda 
can be more easily obtained from the Solvay process soda ash 
than from Le Blanc soda ash. In the case of Solvay soda ash 
it is not necessary to remove the impurities always character¬ 
istic of the commercial products of the Le Blanc process. 

45. Although the production of caustic lye from soda ash 
by the soap maker may be effected at nominal cost, the use 
of the solid caustic, aside from other considerations peculiar 
to each works that may determine the installation of a caustici- 
zing plant, possesses superior advantages regarding cleanliness 
and convenience of working. The commercial production of 
solid caustic dates from 1854, at which time improvements 
introduced in its manufacture by William Gossage, in Eng¬ 
land, resulted in its more general use, although in a very 
impure state, by soap manufacturers and paper makers. 
Artificial alkali was first used in the manufacture of soap in 
1823. It was manufactured in England by James Muspratt 
and according to the Le Blanc process. The Lancashire 
soap boilers were loath to accept this new and purer article, 
and it was only after Muspratt had distributed gratis scores 
of tons of Le Blanc soda that they became convinced of the 
superior economy of artificial over natural soda. The use 
of the sheet-iron drums was introduced by Thompson in 
1857, this innovation being a most welcome improvement over 
cooling the liquid caustic on iron slabs and subsequently break¬ 
ing it into pieces and packing in barrels for shipment. 

46. Causticization of Soda Ash in the Soap Factory. 
The causticizing plant consists essentially of a converting 


MANUFACTURE OF SOAP, PART 1 


33 


kettle, in which the chemical reaction indicated in Art. 44 
is carried out, and a filter for the separation of the lime 
mud. The causticizing plant is shown in its essential char¬ 
acteristics in Fig. 4. It is required to causticize the soda 
ash as completely as possible, and for this reason the lime 
should be free from impurities. In causticizing a ton of 
soda ash, lime containing 2 per cent, of calcium sulphate 
will convert 42 pounds of a ton of soda ash into the less valu¬ 
able product, sodium sulphate. 

The solution of the soda ash in water is effected in the 
converting kettle a with the aid of live steam introduced 



through the pipe b, and the required amount of lime is shoveled 
in. The contents of the kettle is thoroughly agitated and 
boiled up with live steam, after which it is allowed to settle. 
The supernatant liquor is then pumped off through the swing- 
joint pipe c. The lime precipitate, or mud, is boiled up with 
water and dropped on the filter D , where it is drained and 
washed. In some instances this lime waste, known as whiting , 
is recovered. This product is utilized in the manufacture of 
putty and in the paper industry as a make-weight, or filler. 
































































34 


MANUFACTURE OF SOAP, PART 1 


47. As shown by experiments carried out by Lunge, the 
results of which are given in Table III, the causticization is 
most complete with dilute solutions of soda ash. 

It is claimed for the apparatus shown in Fig. 4 that a 
caustic-soda solution of 14.5° Baume, equivalent to 600 
pounds of 77-per-cent, caustic, can be obtained from 800 
pounds of 58-per-cent, soda ash and 650 pounds of lime. 
As a solution of caustic soda of this density is too dilute 
when soap is boiled on open steam, evaporation of the weak 

TABLE III 


COMPLETENESS OF CAUSTICIZATION OF SOLUTIONS OF 
SODA ASH OF VARIOUS STRENGTHS (LUNGE) 


Per Cent. Na 2 C0 3 
in Liquor 

Specific Gravity 
Before Causticizing 

Per Cent. Na 2 C0 3 Made 
Caustic by Treatment 

Test No. 1 

Test No. 2 

2 

1.022 at 15 0 C. 

99.4 

99-3 

5 

1.052 at 15 0 C. 

99.0 

99.2 

IO 

1.107 at 15 0 C. 

97.2 

97.4 

12 

1.127 at 15 0 C. 

96.8 

96.2 

14 

1.150 at 15 0 C. 

94-5 

95-4 

16 

1.169 at 30° C. 

93-7 

94.0 

20 

1.215 at 30° C. 

90.7 

91.0 


caustic lye to the required density is resorted to when the 
facilities of the factory permit. 

48. Electrolytic Production of Caustic Soda. —It 

has been long known that when a current of electricity is 
passed through a solution of sodium chloride the same is 
decomposed into its positive and negative ions, appearing, 
respectively, at the negative and positive poles, or, as they 
are called, the cathode and the anode. 

When a solution of sodium chloride is thus electrolyzed, 
chlorine will appear at the anode and sodium at the cathode. 
Chlorine, being gaseous, will either pass into solution or be 
discharged into the atmosphere; sodium, being a very active 













MANUFACTURE OF SOAP, PART 1 


35 


element, immediately decomposes the water surrounding the 
cathode, forming sodium hydrate and liberating hydrogen. 
Many varieties of electrolytic cells have been designed, 
with varying degrees of success, to serve as a commercial 
producer of caustic soda and chlorine. The chief mechanical 
difficulty in the production of a satisfactory electrolytic cell 
lies in the character of the diaphragm, which serves to separate 
the products liberated from the positive and negative poles. 
Chlorine must not be allowed to diffuse through the brine, 
as secondary reactions are set up. The problem is to find 
a satisfactory medium that will prevent the diffusion of the 
liberated products and at the same time offer no resistance 
to the passage of the electric current. 


49 . Castner Electrolytic Process for the Produc¬ 
tion of Caustic Soda and Chlorine. —In the Castner 



cell, mercury is used to separate the chlorine liberated at 
the positive pole, or anode, and the sodium liberated at the 
negative pole, or cathode. The cell, as shown in Fig. 5, is 
essentially a box made of slate slabs and divided into three 
compartments marked e, f, g. Compartments e and g contain 
the salt solution and the carbon anodes a, while compart¬ 
ment / contains the caustic-soda solution and the iron cathode 
c. Sufficient mercury covers the bottom of the cell to alloy 
with the sodium as it is liberated. By means of the cam b 
the cell is subjected to a slight oscillation on the pivot d. 

































































































36 


MANUFACTURE OF SOAP, PART 1 


In this manner, the sodium-mercury amalgam is carried into 
compartment /, where the amalgam acts as the anode to the 
iron cathode c, the sodium being set free to combine with the 
water in compartment /. The electrolysis of the brine 
takes place in compartments e and g. The sodium immedi¬ 
ately alloys with the mercury, which serves to carry the 
alkali into compartment /, where the formation of caustic 
soda takes place. A regulated supply of water is run into 
the middle compartment to^ combine with the sodium, which 
is allowed to flow out as a dilute caustic-soda solution in 
corresponding volume. The chlorine gas is removed by 
exhaustion from compartments e and g. 

The Castner process is employed industrially at Niagara 
Falls for the production of caustic soda and bleaching powder, 
and appears to be one of the most successful devices of its 
kind that has yet been developed. 

50 . Comparison of the Methods of Alkali Manu¬ 
facture. —The Le Blanc process for the manufacture of 

commercial alkali products is able to survive in the face 

/ 

of the cheaper Solvay process with its absence of waste 
products only by virtue of its production of hydrochloric-acid 
gas as a by-product. 

So long as no cheaper method for the manufacture of 
muriatic acid is developed, the Le Blanc process will continue 
to be an important industry. In other respects, the Solvay 
process possesses every advantage. 

The several electrolytic processes that have taken practical 
shape during the past few years have assumed a productive 
importance that will increase with each succeeding year. 
The problem of their commercial success is being gradually 
brought to a satisfactory solution, and what influence they 
may exert on the firmly established chemical processes is 
being watched with no little interest. As a producer of 
alkali, it is not likely that the ammonia process will be assailed. 
The older chemical process, which has so long monopolized 
the manufacture of bleaching powder, has most to fear from 
the growth of the electrolytic methods. 


MANUFACTURE OF SOAP, PART 1 


37 


To sum up the essential differences between the chemical 
and electrolytic methods for the production of sodium com¬ 
pounds, it may be stated that the electrolytic process is direct, 
clean, labor saving, and free from worthless by-products. 
On the other hand, its units of plant are small, troublesome, 
expensive, and rapidly deteriorate with use. The chemical 
process provides a large output with comparatively few large 
units of plant of rather simple construction. The repairs, 
though costly, are not numerous and do not have to be 
applied to a vast number of small pieces of apparatus. To 
the disadvantage of the chemical process, it may be said to 
be arduous and that fairly skilled labor is required for its 
operation; also that a number of by-products, invariably 
troublesome and of little or no value, are produced. 

51. Grading of Soda Ash. —The system of grading 
soda ash and caustic soda is based on the molecular com¬ 
position of these bodies. The quotations of the various 
grades in terms, respectively, of 48-per-cent, alkali and 
60-per-cent, caustic is handed down from the early Le Blanc 
days and is an evidence of the highest grades of those products 
they were then able to produce mechanically. The molecular 
weight of sodium carbonate, Na 2 C0 3 , is 106, composed of 
62 parts by weight, or 58.49 per cent., of Na 2 0, the remainder 
being C0 2 . A soda ash that contains 58.49 per cent, of 
Na 2 0 is therefore chemically pure, this percentage being 
equivalent to 100 per cent, of Na 2 C0 3 . A 58-per-cent, 
alkali should contain 58 per cent, of Na 2 0 or its equiva¬ 
lent, 99.16 per cent, of Na 2 C0 3 ; likewise, a 48 per-cent, 
alkali should contain 48 per cent, of Na 2 0 or its equiva¬ 
lent, 82 per cent, of Na 2 C0 3 . The reduction of any grade 
of soda to that of 48 per cent, is effected by admixture with 
common salt. Following are presented for comparison two 
fairly representative analyses of these two standard grades of 
soda ash: 

Grade Per Cent. Per Cent. Per Cent. Per Cent. F2O3AI2O3 CaC0 3 rj n 
Per Cent. Na 2 C0 3 NaCl NaiSO* NaOH Si0 2 MgC0 3 

48 60.64 28.34 4.35 1.29 1.12 Traces 4.26 

58 98.72 .54 .20 .10 .17 .26 


38 


MANUFACTURE OF SOAP, PART 1 


52. Grading- of Caustic Soda. —Caustic soda occurs 
on the market in a variety of grades and is sold on the basis 
of 60 per cent, of Na 2 0. Caustic soda as a product of the 
alkali industry did not appear until 30 years after the industry 
was established in Great Britain, and the expression of its 
quality in the same terms as that of soda ash might therefore 
be expected. The molecular weight of caustic soda is 40; to 
arrive at sodium oxide, Na 2 0, as an expression of the cus¬ 
tomary unit, 2 molecules, with a total molecular weight of 
80, are used. In 2 NaOH there are 63 parts, or 77.5 per cent, 
of Nc^O, the remainder being H 2 0. Therefore, a chemically 
pure caustic soda contains 77.5 per cent, of Na 2 0, or its 
equivalent, 100 per cent, of NaOH. Following is given for 
comparison the percentage of the essential ingredient corre¬ 
sponding to, but never present in, the various grades of 
caustic commonly found in the market: 


Grade 


Per Cent. 
NaOH 


60. 77.42 

70. 90.32 

72. 92.90 

74. 95.48 

76. 98.06 

77/.. 99.35 

77.5. 100.00 


Sodium chloride, sodium carbonate, and sodium sulphate, 
in varying proportions, constitute chiefly the remainder of 
the ingredients. With the present system of grading based 
on the chemical determination of the total alkali, the Na 2 0 
content of the Na 2 C0 3 is estimated with the Na 2 0 in terms of 
which the caustic soda, or NaOH , is expressed. With this 
method of expressing the quality of the caustic soda, the 
soap maker has just cause for complaint in that a variable 
percentage of an ingredient (sodium corbonate) not so valuable 
as the caustic soda is included in the total percentage of the 
essential ingredient present. The following is an industrial 
analysis of a sample of commercial caustic purporting to be 
of 74-per-cent, quality: 









MANUFACTURE OF SOAP, PART 1 


39 


Per Cent. 


Total alkali, Na 2 0 .74.18 

Total alkali, present as NaOH .69.88 

Caustic alkali, NaOH .90.18 

Combined alkali, Na 2 CO$ . 7.35 

Sodium chloride, NaCl . 2.02 


This analysis indicates the sample to be of substantially 
70-per-cent, quality. The difference between the sodium 
hydroxide actually present and that claimed, namely, 4.30 per 
cent. Na 2 0, is due to the 7.35 per cent, of Na 2 COz, this being 
estimated as its equivalent, 4.30 per cent, of Na 2 0, in the 
total sodium oxide. As more or less carbonate is invariably 
present in all commercial caustic, especially in the lower 
grades, the system of including it in the expression of the 
quality of this product is open to severe criticism. Quota¬ 
tions of quality are thus confessedly a misrepresentation. 
The only rational method is the expression of the Na 2 0 as 
free caustic, or preferably units of NaOH. 

This would be an absolute index of the value of the caustic 
as a saponifying agent, and not, as by the method in vogue, 
an uncertain approximation of the same. English degrees 
indicate the strength of the ash or the caustic in terms of 
Na 2 0, but owing to an error in atomic weights, English 
analyses indicate a greater percentage of Na 2 0 than is pres¬ 
ent. This error has become so firmly established by tradition 
that modern ideas have been unable as yet to eliminate it. 
In Germany and Russia the strength is expressed in terms 
of sodium carbonate. This system is perfectly rational 
when applied to soda ash, but is inconsistent when applied 
to caustic. The expression of the value of commercial caustic 
soda in terms of an impurity is certainly not conducive to 
clear ideas on the subject, even though, in so far as the soap 
industry is concerned, this impurity is positively worthless 
as a saponifying agent for neutral glycerides. 

53. The superior advantages and the economy of high- 
grade caustic need no argument. It is true of this product 
that the best, within certain limits, is the cheapest. The 







40 


MANUFACTURE OF SOAP, PART 1 


variation in price arises from the slight differences in cost of 
production of the lower grades, combined, for those grades, 
with the proportionally greater cost of packages, transporta¬ 
tion, etc. 

The total charges contingent on marketing a 60-per-cent, 
caustic are the same as those of a 70-per-cent., although 
the former contains considerably less of the essential ingredi¬ 
ent; also, the cost of production of a 70-per-cent, caustic is 
but little more than that of a 60-per-cent. The increased 
cost of production of the higher grades, namely, 74 per cent, 
and 76 per cent., makes necessary a higher price, which is 
less than it would be if cost of marketing were correspondingly 
increased. 

54. Preparation of Caustic-Soda Lye. —The solid 
caustic soda is delivered at the works in the familiar sheet- 
iron drums, containing usually about 675 pounds. The 
dissolving of the solid caustic is a simple operation. The 
method employed in effecting solution, the arrangement of 
the tanks, and the system of transferring the lye, vary with 
each establishment. 

The work of solution is facilitated by inserting a false 
bottom or cage in the bottom of the solution tank. The 
usual practice is to make a strong lye of 36°-40° Baume, and 
dilute as needed. To make this strong lye the proper amount 
of water is run into the tank. The caustic soda in drums is 
rolled up to the tank, the plates on the heads are cut off and 
about twenty slashes with an axe made into the drum along its 
length. The drums are then lowered to the cage. The main 
draw-off cock is placed about 4 inches above the bottom of the 
tank so that the mud is not drawn when the lye is used. 
By making the solution in the afternoon it will be ready for use 
in the morning. At that time, the drums are taken out, 
examined for undissolved caustic, washed, and broken up for 
sale as scrap. 

With this arrangement, a natural circulation of liquor of 
different densities is set up, with the result that weak liquor 
continually rises to the surface, while the saturated liquor, 


MANUFACTURE OF SOAP, PART 1 


41 


by virtue of its greater density, goes to the bottom. This 
eliminates the mechanical agitation that is necessary when the 
solid caustic is allowed to rest on the bottom of the tank. 

TABLE IV 

PERCENTAGE OF SODIUM HYDRATE, NaOIT , IN DYES OF 
DIFFERENT DENSITIES, MADE FROM CAUSTIC 
OF VARIOUS GRADES 


Specific 

Gravity 

Degrees 

Baume 

77 a % 
%NaOH 

76% 

%NaOH 

74 Vo 

%NaOH 

1.075 

10 

6.55 

6.42 

6.25 

i.091 

12 

8.00 

7.84 

7.63 

1.116 

15 

10.06 

9.86 

9.60 

1.142 

18 

12.64 

12.40 

12.07 

1.162 

20 

14-37 

14.09 

13.72 

1.180 

22 

I 5 . 9 I 

15-61 

15.19 

1.210 

25 

18.58 

18.23 

17.74 

1.241 

28 

21.42 

20.99 

20.44 

1.263 

30 

23.67 

23.21 

22.60 

1.320 

35 

28.83 

28.28 

27-53 

Specific 

Degrees 

72% 

70 % 

60 % 

Gravity 

Baume 

%NaOII 

%NaOH 

%NaOH 

1.075 

10 

6.08 

5.91 

5.06 

I.091 

12 

7-43 

7.22 

6.19 

I.Il6 

15 

9-34 

9.08 

7.78 

I.142 

18 

11.74 

II.41 

9.78 

I.162 

20 

13.35 

12.97 

II.12 

I.180 

22 

14.78 

14.36 

12.31 

I 210 

25 

17.27 

16.78 

14.38 

I.24I 

28 

19.89 

19.33 

16.57 

I.263 

30 

21.99 

21-37 

18.32 

1.320 

35 

26.79 

26-04 

22.31 


55. In the preparation of caustic lyes of different den¬ 
sities from various grades of caustic, the effect of the 






























TABLE V—SPECIFIC GRAVITY OF CAUSTIC-SODA SOLUTIONS 

AT 15° C. (LUNGE) 


Specific 

Gravity 

Degrees 

Baume 

Degrees 

Twaddell 

Per Cent. 
NazO 

Per Cent. 
NaOH 

1 Cubic Meter Con¬ 
tains Kilograms 

NazO 

NaOH 

I.007 

I 

1-4 

O.47 

O.61 

4 

6 

1.014 

2 

2.8 

0-93 

1.20 

9 

12 

1.022 

3 

4-4 

i -55 

2.00 

16 

21 

1.029 

4 

5-8 

2.10 

2.71 

22 

28 

1.036 

5 

7.2 

2.60 

3-35 

27 

35 

1.045 

6 

9.0 

3.10 

4.00 

32 

42 

1.052 

7 

10.4 

3.60 

4.64 

38 

49 

1.060 

8 

12.0 

4.10 

5.29 

43 

56 

1.067 

9 

13-4 

4-55 

5.87 

49 

63 

1-075 

10 

15-0 

5.08 

6.55 

55 

70 

1.083 

11 

16.6 

5.67 

7.31 

61 

79 

1.091 

12 

18.2 

6.20 

8.00 

68 

87 

1.100 

13 

20.0 

6.73 

8.68 

74 

95 

1.108 

14 

21.6 

7.30 

9.42 

81 

104 

1.116 

15 

23.2 

7.80 

10.06 

87 

112 

1.125 

16 

25.0 

8.50 

10.97 

96 

123 

1.134 

17 

26.8 

9.18 

11.84 

104 

134 

1.142 

18 

28.4 

9.80 

12.64 

112 

144 

1.152 

19 

30.4 

10.50 

13-55 

121 

156 

1.162 

20 

32.4 

11.14 

14.37 

129 

'67 

i. 171 

21 

34-2 

II .73 

15.13 

137 

177 

1.180 

22 

36.0 

12.33 

15.91 

146 

188 

1.190 

23 

38.0 

13.00 

16.77 

155 

200 

1.200 

24 

40.0 

13.70 

17.67 

164 

212 

1.210 

25 

42.0 

14.40 

18.58 

T 74 

225 

1.220 

26 

44-0 

15.18 

19.58 

185 

239 

1.231 

27 

46.2 

15.96 

20.59 

196 

253 

1.241 

28 

48.2 

16.76 

21.42 

208 

266 

1.252 

29 

50.4 

17.55 

22.64 

220 

283 

1.263 

30 

52.6 

18.35 

23.67 

232 

299 

1.274 

3 i 

54-8 

19.23 

24.81 

245 

316 

1.285 

32 

57 -o 

20.00 

25.80 

257 

332 

1.297 

33 

59-4 

20.80 

26.83 

270 

348 

1.308 

34 

61.6 

21.55 

27.80 

282 

364 

1.320 

35 

64.0 

22.35 

28.83 

295 

381 

1-332 

36 

66.4 

23.20 

29-93 

309 

399 

1-345 

37 

69.0 

24.20 

31.22 

326 

420 

1-357 

38 

71.4 

25.17 

32.47 

342 

441 

1-370 

39 

74.0 

26.12 

33-69 

359 

462 

1.383 

40 

76.6 

27.10 

34 96 

375 

483 

1-397 

4 i 

79-4 

28.10 

36.25 

392 

506 

1.410 

42 

82.0 

29.05 

37-47 

410 

528 

1.424 

43 

84.8 

30.08 

38.80 

428 

553 

1.438 

44 

87.6 

31.00 

39-99 

446 

575 

'•453 

45 

90.6 

32.10 

41.41 

466 

602 

1.468 

46 

93-6 

33-20 

42.83 

487 

629 

1-483 

47 

96.6 

34-40 

44.38 

5 io 

658 

1.498 

48 

99.6 

35-70 

46.15 

535 

691 

I- 5 I 4 

49 

102.8 

36.90 

47.60 

559 

721 

1 530 

50 

106.0 

38.00 

49.02 

58 i 

750 


42 



































MANUFACTURE OF SOAP, PART 1 


43 


impurities, chiefly sodium chloride, sodium carbonate, and 
sodium sulphate, is to reduce the active value of the solu¬ 
tion for the specific gravity indicated. This reduction in 
saponifying power is least for the highest grades and greatest 
for the lowest, as a natural result of the increased percentage 
of these impurities present. There is arranged in Table IV 
the percentage of sodium hydrate present in lyes of different 
densities, made from the usual grades of caustics, correspond¬ 
ing to the densities of lye made from chemically pure caus¬ 
tic. It is assumed that the total alkali which never actually 
occurs, is present entirely as caustic. The figures stated, for 
reasons previously given, are slightly higher than would be 
found in practice. However, this table possesses some value 
as a basis of comparison, and for many technical purposes the 
figures are suficiently accurate. 

In the preparation of caustic-soda lye in the kettle room, 
the number of drums of caustic soda and the quantity of 
water required to furnish a lye of a certain density will be 
learned by experience. In Table V are given the densities of 
caustic-soda solutions made from chemically pure caustic soda. 

56. Use of Caustic-Soda Lye. —The caustic-soda lye 
tank is usually situated in the kettle or soap-boiling room 
with an elevation of 3 or 4 feet above the tops of the kettles. 
It is placed at one end and piped to reach each kettle. The 
piping is arranged with stop valves so as not to interfere with 
any other boiling. Below the discharge cock, a water line is 
connected directly into the lye line running to the kettles. 
This makes it possible to deliver lye of any strength by control¬ 
ling the lye and water valves. The soap boiler is provided 
with a Baume hydrometer and draws the lye for test at the 
kettle into a cylinder or hydrometer jar as it is being delivered. 
A very good form of jar can be made from short pieces of 
pipe and fittings as shown in Fig. 6, wherein a may be regarded 
as a handle. When taking a sample the jar proper, 6, is 
completely filled to c and the hydrometer dropped in, and the 
reading taken. By this means the lye is kept at the strength 
desired and is at all times under complete control. 


44 


MANUFACTURE OF SOAP, PART 1 


57. Caustic Potasli.—Potash, or crude potassium car¬ 
bonate, was originally obtained from the ashes of seaweeds, 
and before the development of the Le Blanc process it pro¬ 
vided the only saponifying agent then available. Later, 
wood ashes, beet-sugar residues, and wool scourings formed 
the chief commercial source. The various potassium salts 
are now obtained chiefly from the mineral carnallite, which 
is composed of the chlorides of potassium and magnesium 
with water of crystallization. Carnallite, with other min¬ 
erals composed of chlorides and sulphates of the alkali and 

alkaline earth metals, occurs in immense 
deposits near Stassfurt, Germany. 

Caustic potash is manufactured from 
carnallite by the Le Blanc process. The 
potassium chloride is converted into potas¬ 
sium sulphate by treatment with sulphuric 
acid. A mixture is then obtained that is 
analogous to the crude Glauber’s salt of the 
Le Blanc process. This mixture is fused 
with limestone and coal, and the resulting 
mass lixiviated with water. The solution 
of potassium carbonate thus obtained is 
causticized with lime, and a solution of 
caustic potash results. This caustic liquor 
is removed, evaporated to dryness, and 
fused. While molten it is run into drums 
and comes into commerce as caustic pot¬ 
ash. It is not so uniform in its composition as the corre¬ 
sponding sodium compound. Commercial caustic potash is a 
mixture of the following substances: 

Per Cent. 

Carbonate and hydrate of potassium .... 80 to 95 


Chlorides of sodium and potassium. 5 to 10 

Sulphate of potassium. 5 to 15 

Insoluble matter.1.5 to 3 


A good caustic potash is generally opaque and of a dull- 
gray slate or bluish color, often streaked with red or greenish 
stains. It has a powerful affinity for moisture, and on expo- 



























TABLE VI—SPECIFIC GRAVITY OF SOLUTION OF CAUSTIC 

POTASH AT 15 ° C. (LUNGE) 


Specific 

Gravity 

Degrees 

Baume 

Degrees 

Twaddell 

Per Cent. 
KzO 

Per Cent. 
KOH 

1 Cubic Meter Contains 
Kilograms 

KiO 

KOH 

1.007 

I 

1.4 

•7 

•9 

7 

9 

1.014 

2 

2.8 

1.4 

1-7 

14 

17 

1.022 

3 

4.4 

2.2 

2.6 

22 

26 

I.029 

4 

5.8 

2-9 

3-5 

30 

36 

1.037 

5 

7-4 

3-8 

4-5 

39 

46 

1.045 

6 

9.0 

4-7 

5-6 

49 

58 

I.052 

7 

10.4 

5-4 

6.4 

57 

67 

I.060 

8 

12.0 

6.2 

7-4 

66 

78 

I.067 

9 

13-4 

6.9 

8.2 

74 

88 

1.075 

10 

15-0 

7-7 

9.2 

83 

99 

I.083 

11 

16.6 

8-5 

10.1 

92 

109 

1.091 

12 

18.2 

9.2 

10.9 

100 

119 

1.100 

13 

20.0 

10.1 

12.0 

hi 

132 

1.108 

14 

21.6 

10.8 

12.9 

119 

143 

1.116 

15 

23.2 

11.6 

13.8 

129 

153 

1.125 

16 

25.0 

12.4 

14.8 

140 

167 

1.134 

17 

26.8 

13.2 

15-7 

150 

178 

1.142 

18 

28.4 

13-9 

16.5 

159 

188 

1.152 

19 

30.4 

14.8 

17.6 

170 

203 

1.162 

20 

32.4 

15.6 

18.6 

181 

216 

1.171 

21 

34-2 

16.4 

19-5 

192 

228 

1.180 

22 

36.0 

17.2 

20.5 

203 

242 

1.190 

23 

38.0 

18.0 

21.4 

214 

255 

1.200 

24 

40.0 

18.8 

22.4 

226 

269 

1.210 

25 

42.0 

19.6 

23-3 

237 

282 

1.220 

26 

44-0 

20.3 

24.2 

248 

295 

I.231 

27 

46.2 

21.1 

25.1 

260 

309 

1.241 

28 

48.2 

21.9 

26.1 

272 

324 

1.252 

29 

50.4 

22.7 

27.0 

284 

338 

I.263 

30 

52.6 

23-5 

28.0 

297 

353 

1.274 

3 i 

54-8 

24.2 

28.9 

308 

368 

1.285 

32 

57-0 

25.0 

29.8 

321 

385 

1.297 

33 

59-4 

25.8 

30.7 

335 

398 

1.308 

34 

61.6 

26.7 

31.8 

349 

416 

1.320 

35 

64.0 

27-5 

32.7 

363 

432 

1.332 

36 

66.4 

28.3 

33-7 

377 

449 

1-345 

37 

69.0 

29-3 

34-9 

394 

469 

1.357 

38 

71.4 

30.2 

35-9 

410 

487 

1.370 

39 

74.0 

31.0 

36.9 

425 

506 

1-383 

40 

76.6 

31.8 

37-8 

440 

522 

1-397 

4 i 

79-4 

32.7 

38.9 

457 

543 

1.410 

42 

82.0 

33-5 

39-9 

472 

563 

1.424 

43 

84.8 

34-4 

40.9 

490 

582 

1.438 

44 

87.6 

35-4 

42.1 

509 

605 

1-453 

45 

90.6 

36.5 

43-4 

530 

631 

1.468 

46 

93-6 

37-5 

44.6 

549 

655 

1.483 

47 

96.6 

38.5 

45-8 

57 i 

679 

1.498 

48 

99.6 

39-6 

47.1 

593 

706 

1 .514 

49 

102.8 

40.6 

48.3 

615 

731 

1-530 

50 

to6.o 

4 i .5 

49.4 

635 

756 


45 


394—4 

























46 


MANUFACTURE OF SOAP, PART 1 


sure to the air, it deliquesces rapidly and soon becomes pasty. 
Sometimes, it presents a whitish appearance in the center of 
the drum, and occasionally it is honeycombed. That which 
contains a large porportion of salts is usually crystaline 
and very compact. Its high cost militates against its more 
general use as a saponifying agent; and it is used very little 
today in soap manufacture. On exposure to the air, its 
solutions rapidly absorb carbon dioxide, with the formation 
of the acid carbonate. As a chemical agent it is more active 
than caustic soda. Caustic potash improves the quality of 
all soaps of which it is an ingredient. It cannot be used in 
settled soap manufacture with sodium chloride as the grain¬ 
ing agent, because an interchange of alkalies would take 
place and much of the potassium would be lost as the 
chloride. Soaps containing it are milder in their de¬ 
tersive action, will stand more filling without efflores¬ 
cence, and possess a tougher texture. 

By virtue of their milder detersive action on animal 
and vegetable fibers, potash soaps—usually soft soaps— 
find wide application in the textile industry. 

In Table VI is given the specific gravity of solu¬ 
tions of caustic potash at 15° C., according to Lunge. 


MEASUREMENT OF THE DENSITY OF LIQUIDS 

58. The specific gravity of a liquid or solid is the 
expression of the relation between the weight of the 
liquid or solid and the weight of an equal volume of 
pure water at a definite temperature, usually 15° C. 
The most convenient and practical means of ascertain¬ 
ing the strength of solutions of carbonated and caustic 
alkalies is to determine their specific gravity with a 
hydrometer. As shown in Fig. 7, the hydrometer is simply 
a closed tube with a bulb blown in one end, containing a 
paper scale and filled with shot or murcury. When placed in 
a liquid, the weighted bulb enables the hydrometer to float in 
an upright position. The Baume and Twaddell hydrometers 
are the instruments most commonly used, the Baume 



Fig. 7 















MANUFACTURE OF SOAP, PART 1 47 

hydrometer in America and the Twaddell hydrometer in 
England. 

With the latter instrument, the density of pure distilled 
water is represented by zero, and the scale is graduated in such 
a manner that the specific gravity of the liquid may be cal- 

TABLE VII 

SPECIFIC GRAVITY AND DEGREES BAUME (AMERICAN 
STANDARD) FOR LIQUIDS HEAVIER THAN WATER 

AT 60 ° F. (OLSEN) 


Degrees 

Baum6 

Specific 

Gravity 

Degrees 
Bau me 

Specific 

Gravity 

Degrees 

Baume 

Specific 

Gravity 

O 

I .oooo 

24 

1.1983 

48 

1.4948 

I 

1.0069 

25 

1.2083 

49 

1.5104 

2 

1.0140 

26 

1.2185 

50 

1.5263 

3 

1.02 I I 

27 

1.2288 

5i 

1.5426 

4 

I.O284 

28 

1-2393 

52 

I.559I 

5 

1-0357 

29 

1.2500 

53 

I.5761 

6 

1.0432 

30 

1.2609 

54 

1-5934 

7 

1.0507 

31 

1.2719 

55 

1.6111 

8 

1.0584 

32 

1.2832 

56 

1.6292 

9 

1.0662 

33 

1.2946 

57 

1.6477 

IO 

1.0741 

34 

1.3063 

58 

1.6667 

11 

1.0821 

35 

1.3182 

59 

1.6860 

12 

1.0902 

36 

1-3303 

60 

1.7059 

13 

1.0985 

37 

1.3426 

61 

1.7262 

14 

1.1069 

38 

i.355i 

62 

1.7470 

15 

1.1154 

39 

1.3679 

63 

1.7683 

16 

1.1240 

40 

1.3810 

64 

1.7901 

17 

1.1328 

4 1 

1.3942 

65 

1.8125 

18 

1.1417 

42 

1.4078 

66 

1.8354 

19 

1.1508 

43 

1.4216 

67 

1.8590 

20 

1.1600 

44 

1.4356 

68 

1.8831 

21 

1.1694 

45 

1.4500 

69 

1.9079 

22 

1.1789 

46 

1.4646 

70 

1-9333 

23 

1.1885 

47 

1.4796 




culated by multiplying the number of degrees registered on the 
scale by .005 and adding the product to 1; thus, the density of 
a liquid indicating 100° Twaddell would be 100X.005 
+ 1.000, or 1.500. The Twaddell hydrometer is a direct- 
reading instrument. This means that the reading on the 






















48 


MANUFACTURE OF SOAP, PART 1 


scale shows the specific gravity of the liquid directly as com¬ 
pared with pure water at the definite temperature. 

The Baume hydrometer is adapted for the determination 
of the specific gravity of liquids, either heavier or lighter than 
water (see Tables VII and VIII). The scale used is arbitrary 


TABLE VIII 

SPECIFIC GRAVITY AND DEGREES BAUMlS FOR LIQUIDS 
LIGHTER THAN WATER AT 60 ° F. (OLSEN) 


Degrees 

Baum6 


10 

11 
12 

13 

14 

15 

16 

17 

18 

19 

20 
21 
22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 


Specific 

Gravity 


I .OOOO 

.9929 

•9859 

.9790 

.9722 

•9655 

•9589 

.9524 

•9459 

.9396 

•9333 

.9272 

.9211 

.9150 

.9091 

.9032 

•8974 

.8917 

.8861 

.8805 

•8750 

.8696 

.8642 

.8589 


Degrees 

Baume 


34 

35 

36 

37 

38 

39 

40 

4 1 

42 

43 

44 

45 

46 

47 

48 

49 

50 

51 

52 

53 

54 

55 

56 

57 


Specific 

Gravity 


•8537 

.8485 

•8434 

.8383 

•8333 

.8284 

•8235 

.8187 

.8140 

.8092 

.8046 

.8000 

•7955 

.7910 

•7865 

.7821 

•7778 

•7735 

.7692 

.7650 

.7609 

•7568 

•7527 

•7487 


Degrees 

Baum6 


58 

59 

60 

61 

62 

63 

64 

65 

66 

67 

68 

69 

70 

71 

72 

73 

74 

75 

76 

77 

78 

79 

80 


Specific 

Gravity 


•7447 

.7407 

.7368 

•7330 

.7292 

•7254 

.7216 

.7179 

•7143 

•7107 

.7071 

•7035 

.7000 

.6965 

6931 

.6897 

.6863 

.6829 

.6796 

•6763 

.6731 

.6699 

.6667 


and bears no direct relation to the specific gravity; hence, 
the conversion of the readings into the corresponding specific 
gravity is done by reference to tables prepared for this pur¬ 
pose. In Table IX are given the values of specific gravity 
corresponding to degrees Twaddell and degrees Baume. 

























73 

v 

•O 

•O 

a 

o 

I 

2 

3 

4 

5 

6 

7 

8 

9 

io 

ii 

12 

13 

14 

15 

16 

17 

l8 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

3i 

32 

33 

34 

35 

36 

37 

38 

39 

40 

4i 

42 

43 

1 


TABLE IX 

SPECIFIC GRAVITY, DEGREES TWADDELL, AND 
DEGREES BAUMfi 


Degrees 

Twaddell 

Degrees 

Baum6 

Specific 

Gravity 

Degrees 

Twaddell 

Degrees 

Baume 

Specific 

Gravity 

Degrees 

Twaddell 

Degrees 

Baum6 

Specific 

Gravity 

44 

26.2 

1.220 

88 

44-3 

I .440 

132 

57-7 

I .660 

45 

26.6 

1.225 

89 

44-7 

1-445 

133 

57-9 

1.665 

46 

27 .I 

1.230 

90 

45-0 

1.450 

134 

58.2 

1.670 

47 

27.6 

1-235 

91 

45-3 

1-455 

135 

58.4 

1.675 

48 

28.1 

I. 24 O 

92 

45-7 

1.460 

136 

58.7 

I .680 

49 

28.5 

1-245 

93 

46.0 

1.465 

137 

58.9 

1.685 

50 

29 .O 

1.250 

94 

46.4 

1.470 

138 

59-2 

1.690 

5i 

29-5 

1-255 

95 

46.7 

1-475 

139 

59-5 

1.695 

52 

29-9 

1.260 

96 

47.0 

1.480 

140 

59-7 

I .700 

53 

30.4 

1.265 

97 

47-4 

1.485 

141 

60.0 

1.705 

54- 

30.8 

1.270 

98 

47-7 

1.490 

142 

60.2 

1.710 

55 

31.3 

1-275 

99 

48.0 

1-495 

143 

60.5 

1 .715 

56 

3i-7 

1.280 

100 

484 

1.500 

144 

60.7 

1.720 

57 

32.2 

1.285 

101 

48.7 

1-505 

145 

60.9 

1.725 

58 

32.6 

I. 29 O 

102 

49.0 

1.510 

146 

61.2 

1.730 

59 

33-0 

1.295 

103 

49-3 

I.5I5 

147 

61.4 

1-735 

60 

33-5 

1.300 

104 

49.6 

1.520 

148 

61.7 

I .740 

61 

33-9 

1.305 

105 

49-9 

1.525 

149 

61.9 

1-745 

62 

34-3 

i-3 10 

106 

50.2 

1.530 

150 

62.4 

1.750 

63 

34-7 

I.3I5 

107 

50.6 

1-535 

151 

62.6 

1-755 

64 

35-1 

1.320 

108 

50.8 

1.540 

152 

62.8 

1.760 

65 

35-6 

1.325 

109 

51.2 

.1-545 

153 

63.1 

1.765 

66 

36.0 

1-330 

no 

51-5 

1-550 

154 

63-3 

1.770 

67 

36.4 

1-335 

III 

51.8 

1-555 

155 

63.5 

1.775 

68 

36.8 

I .340 

112 

52.1 

1.560 

156 

63.8 

1.780 

69 

37-2 

1-345 

113 

52.3 

1.565 

157 

64.0 

1.785 

70 

37-6 

1-350 

114 

52.6 

1.570 

158 

64.2 

1.790 

7i 

38.0 

1-355 

H5 

52.9 

1-575 

159 

64.4 

1-795 

72 

38.4 

1 .3 6 ° 

116 

53-2 

1.580 

160 

64.7 

1.800 

73 

38.8 

1.365 

117 

53-5 

1.585 

161 

64.9 

1.805 

74 

39-2 

1-370 

Il 8 

53-8 

1.590 

162 

65.1 

1.810 

75 

39-5 

1-375 

119 

54 * 1 

1-595 

163 

65.2 

1.815 

76 

39-9 

1.380 

120 

54-3 

1.600 

164 

65.3 

1.820 

77 

40-3 

1.385 

121 

54-7 

1.605 

165 

65.5 

1.825 

78 

40.7 

1.390 

122 

54-9 

1.610 

166 

657 

1.830 

79 

41.1 

1.395 

123 

55-2 

1.615 

167 

66.0 

1.835 

80 

4 I -5 

. 1.400 

124 

55-5 

1.620 

168 

66.2 

*.840 

81 

41.8 

1.405 

125 

55-8 

1.625 

169 

66.4 

1.845 

82 

42.2 

1.410 

126 

56.0 

1.630 

170 

66.7 

1.850 

83 

42.5 

I.4I5 

127 

56.3 

1.635 

171 

66.9 

1.855 

84 

42.9 

1.420 

128 

56.6 

1.640 

172 

67.0 

1.860 

85 

43-2 

i.4 2 5 

129 

56.9 

1.645 

173 

67-5 

1.865 

86 

43-6 

1.430 

130 

57-1 

1.650 




87 

44.0 

1-435 

131 

57-4 

1.655 











































50 


MANUFACTURE OF SOAP, PART 1 


CHEMISTRY OF SOAP MANUFACTURE 

59. In the preceding examination of the raw materials of 
soap manufacture there have been considered those bodies 
which carry the two compounds—namely, a glyceride and a 
caustic alkali—that, when in chemical combination, form 
soap. Soap boiling, therefore, consists essentially in bring¬ 
ing a fatty body and a caustic alkali in aqueous solution in 
contact under suitable conditions, whereby a simple chemical 
reaction takes place with the formation of an alkaline salt of 
a fatty acid and the liberation of glycerine. This reaction 
is known as saponification. 

60. For the purpose of explanation, the fatty body will 
be represented by 1 molecule of stearin and the saponifying 
agent by 3 molecules of caustic soda; thus: 

C*H 6 ( C 18 H 3b , 0 2 ) s+ZNaOH = CzH^OH^z^ZCizHzaOzNa 

stearin caustic soda glycerine sodium stearate 

The term saponification is also applicable to a vast number 
of similar chemical changes in which an alcohol is set free 
and an acid is produced, when water is the saponifying agent, 
or an alkaline salt of the fatty acid, that is, soap, when the 
saponifying agent is an alkali. 


GLYCERIDES AND THEIR PROPERTIES 

61. In order to understand thoroughly the soap-making 
properties of the various fats and oils and their behavior in 
the soap kettle, it is necessary to be familiar with the chem¬ 
ical properties of the various glycerides that constitute the 
fats and oils employed in soap manufacture. The variation 
in the amount of alkali absorbed by any particular fat or oil 
arises from differences in the composition of the glycerides 
themselves and from the varying proportions in which the 
glycerides occur in any particular stock. It is a well known 
fact that fats and oils are indefinite mixtures of various 
glycerides, and that the amount of alkali absorbed is influenced 
by the nature of the glycerides characteristic of the stock. 



TABLE X 


ACIDS OF THE ACETIC SERIES-GENERAL FORMULA, C n R 2n1 - 1 COOJT 


Acid 

Formula 

Mol. 

Wt. 

Corresponding 

Glyceride 

Formula 

Mol. 

Wt. 

Per Cent, 
of 

Ha OH 
Ab¬ 
sorbed 

Per Cent, 
of 

Glycerine 
Set Free 

Per Cent, 
of Fatly 
Acids 
Set Free 

Natural Source 

Formic. 

H■ COOH 

46 

Formin 

GiH( 0 -HCO) s 

176 

68.19 

52.28 

78.41 

The acid occurs in bodies of ants, in the stinging pine, and in certain nettles 

Acetic. 

CHi-COOH 

60 

Acetin 

C 3 H 5 ( 0 -CHC 0 ) 3 

2l8 

55.04 

42.20 

82.56 

Occurs naturally only in slight quantities in oil of Euonymus Europcsus. 

Propionic. 

GiHsCOOH 

74 

Propionin 

CsHslO-CuHaCOa 

260 

46.15 

35.38 

85-38 

Occurs in small quantities in the fruit of Gingko biloba. 

Butyric. 

CM-COOH 

88 

Butyrin 

G±H:>{ 0 -CzH 7 C 0 )z 

302 

39-74 * 

30.47 

87.42 

Cow’s butter. 

Valeric. 

CiH-COOH 

102 

V alerin 

CzHs( 0 -CiH 9 C 0 ) 3 

344 

34.88 

26.74 

88.94 

The acid occurs in the animal and vegetable kingdoms, free, and as an ester. 

Caproic. 

CXHn-COOH 

Il6 

Caproin 

CiIh( 0 -GIInCO) 3 

386 

31.09 

23.83 

90.16 

Cow’s butter, coconut, and palm-kernel oils. 

Oenanthylic . . . 

GHwCOOH 

130 

Oenanthylin 

C?J-h{ 0 -GJC 3 C 0 ) 3 

428 

28.04 

21.50 

91.14 

Occurs in small quantities in Kalmus oil. 

Caprylic. 

Ct Ha-COOH 

144 

Caprylin 

CzHs ( O' C7H1 5 CO) 3 

470 

25-54 

19.57 

91.91 

Cow’s butter, coconut, and palm-kernel oils. 

Pelargonic .... 

CsHn-COOH 

158 

Pelargonin 

CsHs(0-CsHnC0)3 

512 

23.44 

17.97 

92.58 

The acid occurs naturally in leaves of Pelargonium roseum. 

Capric. 

GHwCOOH 

172 

Caprin 

C 3 ffs{0-C 9 Hi 9 C0) 3 

554 

21.66 

16.61 

93.13 

Cow’s butter, coconut, and palm-kernel oils. 

Undecylic . . . 

CwHn-COOH 

186 

Undecylin 

GiHdO-CmH2iCO) 3 

596 

20.14 

15.44 

93-63 


Laurie. 

CnH-a-COOH 

200 

Laurin 

CzHs( O- C 11 H 23 CO) 3 

638 

-8.81 

14.42 

94.06 

Spermaceti, tan oil, coconut, and palm-kernel oils. 

Tridecylic .... 

CnH&COOH 

214 

Tridecylin 

C 3 H b (.0-Ci 3 H 3b C0) 3 

680 

17.65 

13.53 

94.41 


Myristic. 

CnHrrCOOH 

22 8 

Myristin 

GiH-AO- C\ ? JhiCO)z 

722 

16.63 

12.75 

94.75 

Spermacetic, muscat butter, coconut, and palm-kernel oils. 

Pentadecatoic . . 

CuHm-COOH 

242 

Pentadecatorin 

CsHsiO-CuHztCOh 

764 

15-70 

12.04 

95.03 


Palmitic. 

CisHn-COOH 

256 

Palmitin 

C 3 H b (OCisH 3 iCO)3 

806 

14.89 

11.41 

95-30 

Associated with stearin and olein in most animal and vegetable fats and oils. 

Margaric. 

CvJhvCOOH 

270 

Margarin 

C 3 Hs{0-CnH 33 C0) 3 

848 

14.16 

10.8s 

95.52 

Seeds of thorn apple. Datura Stramonium. 

Stearic. 

CnH&COOH 

284 

Stearin 

CsHAO-CnHssCOh 

890 

13.48 

10.34 

9572 

See palmitin. 

Nondecylic . . 

CuHstCOOH 

298 

Nondecylin 

C 3 H s (0-Ci S H3,C0) 3 

932 

12.87 

9-87 

95.92 


Arachidic .... 

CwHm-COOH 

312 

Arachidin 

C3Hs(0-Ci 9 H 39 C0) 3 

974 

12.32 

9-44 

96.10 

Characteristic glyceride of peanut oil. 

Medallic. 

C-aHsi ■ COOH 

326 

Medullin 

GJIAO-GJhiCO), 

1,016 

n.81 

9.06 

96.27 

Medullic acid is a mixture of palmitic and stearic acids. 

Behenic. 

C-nHu-COOH 

340 

Behenin 

C3H b {0-C 3 iH i3 CO) 3 

1.058 

11.34 

8.69 

96.40 

Characteristic glyceride of oil of ben. 

Carnaiibic .... 

Cnlhi-COOH 

368 

Carnaubin 

C 3 HAO-C 33 H il CO) 3 

1,142 

10.51 

8.05 

96-65 

Occurs as an ether in combination with the higher alcohols in carnaiibic wax 

Hyenic. 

Cnfh<r COO/I 

382 

Hyenin 

CsJhiO- Ct\IIviCO) 3 

1,184 

10.14 

7-77 

96.79 

Free acid occurs in glandular pouches of the striped hyena. 

Cerotic. 

Cx,Ihr COOH 

410 

Cerotin 

CzHfXO' 

1,268 

9.46 

7.25 

96-99 

Acid occurs in free state in beeswax and carnaiibic waxes. 

Melissic. 

GmHys-COOH 

452 

Melissin 

C3H 5 (0-CnH 5 9C0) 3 

1,394 

8.61 

6.60 

97-25 

Acid occurs in free state in beeswax. 


ACIDS OF THE ACRYLIC SERIES-GENERAL FORMULA, C^^-iCOOH 


Acrylic. 

Crotonlc. 

Angelic, Tiglic . . 
Hypogaric .... 
Oleic. 

GH.1- COOH 

Cz/h- COOH 

CaH v COOH 

CvJGr COOH 

CnH33- COOH 

72 

86 

100 

254 

282 

Olein 

C 3 HAO-C 3 HzCO) 3 

C-Ji;AO- C 3 /hCO) 3 
C 3 /MO-CaHCO) 3 

C 3 Hs( 0- CuJfziiCO) 

C 3 GAO’ CuH 33 CO) 3 

254 

296 

338 

800 

884 

32.54 

15.00 

13-57 

27.22 

11.49 

10.41 

88.76 

95.26 

95-70 

The acid is an oxidation product of acrolein. 

Acid occurs with isocrotonic acid in crude pyroligneous acid. 

Angelic acid occurs in angelica root. Glyceride occurs in croton oil. 

Present in peanut oil. 

The characteristic glyceride of all liquid fats. 

ACIDS OF THE LINOLIC SERIES—GENERAL FORMULA, C n H 2 „- 3 COOH 

Elasomargaric . . 

Linolic. 

CmHvrCOOH 

CnHn- COOH 

266 

280 

Elaeomargarin 

Linolein 

CzHs>(0-C\<!>H29C0)z 

CzH&{ O' CyjH 31 CO) 3 

836 

878 

14-35 

13-67 

] 

ii.oi | 95-69 

10.48 | 95-68 

Occurs in Japanese wood oil. 

Occurs in linseed and other drying oils. 

ACIDS OF THE LINOLENIC SERIES-GENERAL FORMULA, C n H„ n - 6 COOir 

Linolenic. 

CnH&- COOH 

00 

N 

Linolenin 

CzH$( 0 - CnffnCO) 3 

872 

1376 

IO.S5 

95-64 

Occurs in drying oils, especially linseed oil. 


ACIDS OF THE RECINOLEIC SERIES-GENERAL FORMULA, C„ffo„- 2 0 3 


Kecinolelc .... 

CnH 33 OH COOH 

298 

Recinolein 

C^Hh^O' CyjHz2'OH * CO )3 

932 

12.87 

9.87 

95.92 

Characteristic glyceride of castor oil. 


BB 394 2055 A 
















































































































































































• .* . r 






































y 









































































MANUFACTURE OF SOAP, PART 1 


51 


It will be seen from Table X that the amount of alkali 
required for saturation decreases as the molecular weight of 
the glycerides increases. Hence, it will be found that those 
commercial fats and oils in which the glycerides of low mole¬ 
cular weight occur, possess the highest alkali absorption in 
proportion to their weight. 

The greater quantity of salt required for graining the 
soap made from such stock is due to the presence of those 
glycerides of low molecular weight whose greater solubility 
in brine of the sodium salt is a marked characteristic. As 
the glycerides increase in molecular weight, the solubility in 
brine of the soap obtained therefrom diminishes; hence, less 
salt is required for graining. 

Note. —As shown in Organic Chemistry, the homologous character 
of the simple hydrocarbons of the saturated and unsaturated fatty series 
extends to all compounds formed from them, either naturally or artificially. 
The purpose of Table X is to illustrate this property by extending the 
quantitative characteristics of the more important acids to their corre¬ 
sponding glycerides, and more particularly to those employed in soap manu¬ 
facture, which appear in heavy type. This table is of great practical inter¬ 
est from the standpoint of both the candle maker and the soap boiler, 
inasmuch as the most important practical properties of glycerides, namely, 
alkali absorption and glycerine liberation, are set forth in detail. It will 
be seen from the standpoint of the soap maker that to the acetic and 
acrylic series of fatty bodies belong the most important commercial glycer¬ 
ides, namely, stearin, palmitin, and olein, while to the more unsaturated 
series belong those glycerides characteristic of all drying oils, which are the 
special consideration of the paint manufacturer. 

62. The homologous properties of the glycerides men¬ 
tioned in the previous article and shown in Table X, are 
further shown in their practical application in soap making in 
Table XI, in which is indicated the theoretical yield of 
anhydrous soap from the glycerides mentioned. 

63 The reason for the greater yield of soap from coco¬ 
nut oil than from the ordinary animal and vegetable fats is 
thus made clear Not only is there a greater yield of anhy¬ 
drous soap in itself, but by virtue of that higher yield a 
greater degree of hydration and filling is thus permissible. 
In Table XII are given the actual and not the theoretical 
percentages of caustic potash and caustic soda required in 
practice to saponify the commercial fats and oils mentioned. 


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52 





































MANUFACTURE OF SOAP, PART 1 


53 


TABLE XII 

PERCENTAGES OF CAUSTIC POTASH AND CAUSTIC SODA 
TO SAPONIFY COMMERCIAL FATS AND OILS 



Per Cent. KoH 

Per Cent. NaOH 

Almond oil . 

19.5-19.6 

13.9-14 

Bone fat and grease. 

19.1-19.7 

13.6-14 

Butter. 

22.1-23.2 

15.8-16.5 

Castor Oil. 

17.6-18.1 

12.5-13 

Cod oil. 

18.5-21.3 

13.2-15.1 

Cottonseed oil. 

19.1-19.6 

13.6-14 

Coconut oil. 

24.6-26.8 

17.5-19.1 

Hempseed oil . 

19.3 

13.8 

Linseed oil. 

18.7-19.5 

13.3-14 

Lard oil . 

19.2-19.6 

13.7-14 

Niger seed oil. 

18.9-19.1 

13.5-13.6 

Olive oil. 

19.1-19.6 

13.6-14 

Peanut oil . 

19.1-19.6 

13.6-14 

Palm oil . 

19.6-20.2 

14-14.4 

Palm nut oil . 

22-24.7 

15.7-17.7 

Porpoise oil. 

21.6 

15.5 

Poppy seed oil . 

19.3-19.5 

13.8-14 

Rape oil. 

17.1-17.9 

12.2-12.8 

Rosin. 

17-19.3 

12.1-14 

Seal oil. 

18.9-19.6 

13.5-14 

Sesame oil. 

19-19.4 

13.9-14 

Sperm oil. 

12.3-14 

8.8-10 

Tallow.. . .. 

19.3-19.8 

13.7-14.1 

Walnut oil. 

19.6 

14 

Whale oil. 

18.8-22.4 

13.4-16 









































54 


MANUFACTURE OF SOAP, PART 1 


BEHAVIOR OF FATS AND OILS TOWARD 
SAPONIFYING AGENTS 

64. The various fats and oils display different character¬ 
istics in their behavior toward saponifying agents. Moreover, 
the chemical reactions of organic compounds do not proceed 
with the ease and certainty that characterize the reactions 
of inorganic compounds. In effecting combination between 
fats or oils and caustic alkalies in a soap kettle, where in 
many instances the fatty bodies are in excess of 100,000 
pounds, the chemical peculiarities of the bodies undergoing 
change should in every case be thoroughly understood. 

65. In a mixture of fats, the individual fats tend to 
impart their properties to one another. Certain oils, notably 
coconut and palm kernel, require caustic lye of high density 
to effect combination. With others, as tallow and palm oil, 
saponification takes place readily with caustic lye of lower den¬ 
sity. Coconut oil requires a caustic lye of at least 20° Baume, 
while tallow can be completely saponified with lye no stronger 
than 18° Baume. When soap stocks with these characteristics 
are mixed, the requirements of each are modified so that an oil 
requiring for saponification alone a lye of high density enters 
into combination with lye of a density with which it would 
not combine otherwise without the consumption of a great 
deal of time and labor. On the other hand, that stock requir¬ 
ing naturally for ready saponification a lye of low density 
enters readily into combination with a lye of higher density. 
These peculiarities will be considered in due order. 

66. Saponification of Tallow. —Tallow requires a 
caustic lye of comparatively low density for satisfactory 
saponification. A 12° Baume lye, when no subsequent dilu¬ 
tion is made, is considered to give the best results. On 
boiling with open steam, a lye of 18° to 20° Baume is the 
highest density practicable. When open steam is used with 
caustic lye of this density, tallow is the most easily saponified 
of all glyceride soap stocks, and the soap formed is most 
easily grained. 


MANUFACTURE OF SOAP, PART 1 


55 


Sodium stearate, which constitutes the bulk of the anhy¬ 
drous soap made from tallow, is one of the least soluble in 
water of all the alkaline salts of the fatty acids, as it under¬ 
goes practically no change when treated with 10 parts of 
water; neither is its hardness appreciably affected. This 
quality manifests itself in the inferior lathering properties of 
pure tallow soap. 

For this reason other oils are used. In making a laundry 
soap, rosin is added for the same purpose. Furthermore, 

TABLE XIII 


POUNDS OF TALLOW SAPONIFIED BY 100 POUNDS OF 
CAUSTIC SODA OF DIFFERENT DENSITIES MADE 
FROM VARIOUS GRADES OF CAUSTIC 


M 

0) 

Grade of Caustic Soda 

0) 

C 

fro 
0 s 

77i Per Cent. 
NazO 

76 Per Cent. 
MazO 

74 Per Cent. 
NazO 

72 Per Cent. 
NazO 

70 Per Cent. 
NazO 

60 Per Cent. 
NazO 








Cfl 

□ 

Q 

Tallow 

Saponified 

Tallow 

Saponified 

Tallow 

Saponified 

Tallow 

Saponified 

Tallow 

Saponified 

Tallow 

Saponified 


Pounds 

Pounds 

Pounds 

Pounds 

Pounds 

Pounds 

IO 

46.78 

45.86 

44.66 

43-45 

42.24 

36.20 

12 

57-14 

56.03 

54-55 

53-08 

51-59 

48.49 

15 

7 I -85 

70.46 

68.60 

66.74 

64.88 

60.96 

18 

90.02 

88.26 

85.94 

83.62 

81.28 

69.66 

20 

102.64 

IOO.60 

97.95 

95-30 

92.64 

79-39 

22 

113-64 

I I I.40 

108.50 

105.50 

102.60 

87.92 

25 

132-71 

130.IO 

126.70 

123.30 

119.90 

102.70 

28 

i 53 -oo 

150.IO 

146.IO 

I42.IO 

138.10 

118.40 

30 

169.07 

165.80 

161.40 

157.00 

152.60 

130.80 

35 

205.92 

201.90 

196.60 

191.30 

186.00 

159-30 


on aging, a pure tallow soap becomes so hard as to give 
very little lather, so that its use is not economical for either 
household or laundry purposes. The comparative insolubility 
in water of sodium stearate is also shown in the readiness with 
which tallow soap dries. Its presence in admixture with other 
fats imparts firmness, or body, to the soap, thus enabling a 
greater proportion of softer stock, or that fatty acid whose 
sodium salt has a greater affinity for water, to be incorporated. 





























56 


MANUFACTURE OF SOAP, PART 1 


The use of sodium stearate thus increases the amount of water 
that may be incorporated with a soap without an excessive 
sacrifice of firmness. It is the best raw material for the manu¬ 
facture of grained soaps and admits of the greatest yield of all 
the animal soap stocks. With its use, the various chemical 
and physical changes occurring in the soap kettle during the 
process of boiling are well defined and of easy recognition. 

67. In Table XIII is expressed the saponifying power of 
caustic lyes of different densities made from chemically pure 
and ordinary grades of caustic occurring in the market. By 
this table, the amount of stock that can be saponified by any 
quantity of lye of the density and quality given may be 
readily determined within limits of accuracy suitable for all 
technical purposes to which the table may be applicable. 

68. Saponification of Cottonseed Oil. —Refined cot¬ 
tonseed oil saponifies with difficulty and only after continued 
boiling, especially when saponified alone. The absence of 
free fatty acids tends to retard saponification. Combination 
with alkali is hastened when tallow is present, or upon the 
addition of soap scraps. Saponification is best begun with 
a 15° Baume lye. 

Pure cottonseed-oil soap is white, with a firmness deter¬ 
mined largely by its degree of hydration. It consists almost 
entirely of sodium oleate. This compound is soluble in 
10 parts of water, while sodium stearate, as already shown, 
is not appreciably affected by this volume. In accordance 
with its greater solubility in water, sodium oleate has in 
comparison greater and peculiar lathering properties. It 
lathers more readily than does sodium stearate, but instead 
of the firm lather of tallow soap, obtained only after much 
rubbing, it gives a shiny, thin lather peculiar to all soaps 
made of stock consisting largely of olein, for example, Castile 
soap and cottonseed-oil soap stock. Cottonseed oil is gen¬ 
erally used in admixture with varying proportions of tallow 
and grease. 

A good settled soap of cottonseed oil alone is not practicable. 
Soap thus made is thin and lacks the body and durability of 


MANUFACTURE OF SOAP, PART 1 


57 


a tallow soap or a soap made from mixed stock. By the use, 
however, of a large proportion of soda ash and sodium silicate, 
an artificial firmness may be imparted. 

Cottonseed-oil soaps sweat readily, and unless the oil has 
been refined with care, they discolor rapidly and become 
rancid. The brownish or yellowish blotches seen in soaps 
containing cottonseed oil may be traced to the imperfect 
removal of the coloring matter of the seed during the refining 
process. 


69 . Saponification of Coconut and Palm-Kernel 

Oils. —Coconut and palm-kernel oils differ from all fatty 
bodies employed in soap manufacture in the greater quantity 
of alkali required for saponification, in the greater quantity 
of salt required for graining, and in the greater yield of soap 
produced, the quality of which permits the greatest amount of 
hydration and filling. The difficulty of graining these soaps 
with dry salt or brine is overcome by using strong caustic lye 
for graining. 

Pure coconut-oil soap is white, brittle, and hard. The oil 
is a valuable addition to cottonseed oil and tallow, and it 
yields a soap possessing qualities superior to that possessed 
by either stock alone. *It enters into combination with alkali 
with extreme ease, which property especially adapts it for 
soap manufacture by the cold process. 

During saponification considerable heat is evolved, and 
when once begun, saponification takes place with such 
rapidity that the contents of the kettle, unless carefully 
watched, will boil over. On the stock change (stock sapon¬ 
ification), difficulty is often experience in working with coconut 
oil, or a mixture of oils containing coconut oil, the soap mass 
becoming thick easily. This is due to the high absorption 
of water consequent to rapid saponification and may be 
overcome by retarding the rate of combination of caustic 
alkali and oil. This is best effected by adding brine when 
the soap mass shows signs of becoming thick. It may also 
be provided by adding the oil slowly to the caustic alkali 
already in the kettle, at the same time boiling vigorously. 


58 


MANUFACTURE OF SOAP, PART 1 


70. Coconut oil combines with weak and strong caustic 
lyes with equal facility, but in practice in the boiling of 
settled soap, a density of from 20° to 25° Baume is com¬ 
monly used. Coconut-oil soap when hot is very fluid, smooth, 
and transparent; when cold, it becomes so hard as to be cut 
only with difficulty. It dissolves readily in water, yielding 
a quickly formed, profuse, but not permanent, lather. It is 
caustic to the tongue even though no free alkali is present, 
and when used for toilet purposes in excess of actual require¬ 
ments, it irritates and reddens the skin. If coconut oil is 
not completely saponified, the soap made from it soon becomes 
rancid and odorous. It dissolves freely in salt water and is 
the fatty basis of the so-called marine, or salt-water, soaps. 

71. The complex composition of coconut oil suffices to 
explain the peculiarities of its behavior toward saponifying 
agents and the properties of the soap made from it. Coconut 
and palm-kernel oils contain a greater variety and quantity 
of glycerides of fatty acids of low molecular weight than any 
other soap stock. 

As will be seen by referring to Table XI, these bodies possess 
a higher alkali absorption, yield a greater percentage of 
glycerine on saponification, are more soluble in water when 
free and combined with alkali, and, ’in general, possess less 
stable chemical properties than do similar bodies of higher 
molecular weight that occur commercially as soap stock. 

72. Saponification of Palm Oil. —Palm oil, of which 
palmitin is the chief glyceride, finds only limited use as a 
soap stock in the United States. This oil is used chiefly as an 
ingredient of certain toilet-soap bases (for which purpose it is 
well adapted by its perfume) and to disguise the odor of rosin 
in soap of a high rosin content. In Great Britain and conti¬ 
nental Europe, however, it replaces tallow to a large degree. 

Sodium palmitate so closely resembles sodium stearate in 
its chemical properties that the statements concerning the 
properties of the latter salt are directly applicable to it. 
Palm oil saponifies very readily, owing to the high percentage 
of free fatty acids characteristic of the oil. 


MANUFACTURE OF SOAP, PART 1 


59 


73. Saponification of Rosin, or Colopliony. —Rosin 
when in a pure state consists of the anhydrides of the rosinic 
acids, chiefly abietic acid, (C0 2 H ). On boiling, rosin 

is readily transformed into the acid, which combines with 
both carbonated and free alkali. Rosin may be killed, or 
saponified, alone or added after the kettle has been charged 
with tallow. The tallow may be saponified previously or 
both stocks may be killed together. The difficulty with which 
a pure rosin soap separates, or grains, in even a concentrated 
salt solution is the chief reason for its not being saponified 
alone. This is due to the fact that the specific gravity of 
rosin ranges from 1.07 to 1.10, while that of tallow is about .9. 
Soda ash may be used as the saponifying agent. The rosin 
soap thus made is frothy from the liberation of carbonic-acid 
gas, and as a result of the increased volume caused in this 
manner, much kettle space is required to work it. This 
saponification may be carried out by using a separate kettle 
and saponifying one or more charges at one time, pumping out 
the amount needed for each charge. However, where factory 
conditions are such as to warrant the use of soda ash instead 
of caustic soda, a considerable saving is possible, as is shown 
in the following approximate calculation: 

Example. —6,000 pounds rosin X.13 = 7S0 pounds, approximately, 
of 74-per-cent, (see Table XII) caustic soda required for combination; 

$1.75 = $2.16, cost per 100 pounds of 74-per-cent, caustic soda when 
price is $1.75 per 100 pounds for 60 per cent.; $2.16X7.8 hundredweight 
= $16.85, cost of 74-per-cent, caustic soda, required for combination. 

2 NaOH : Na 2 C0 3 = 780 : x 
80 : 106 = 780 : x 

or 

x= 1,033.5 pounds soda ash required for combination. 

1,033.5 X $.0009 = $9.30, cost of soda ash required for combination. 


Caustic soda costs.$16.85 

Soda ash costs..9.30 

Saving in alkali for 6,000 pounds of rosin.$ 7.55 


74. The alkali salts of the rosin acids are very hygro¬ 
scopic and naturally readily soluble in water, and, as should 
be expected, make a very soft soap. They detract from the 
firmness of all soaps in which they enter. Rosin betrays its 
presence in the finished soap by the darker color and by its 

/ 





60 


MANUFACTURE OF SOAP, PART 1 


characteristic odor and stickiness, which latter property is 
due to the marked affinity of the alkaline resinates for moisture. 

This peculiarity manifests itself in the readiness with 
which poorly made rosin soaps sweat. The marked detergent 
property, ready solubility in either hot or cold, soft or per¬ 
manently hard water, and cheapness of the alkaline resinates, 
make them an indispensable addition to the firmer tallow 
soap for domestic purposes. The characteristic odor may be 
ameliorated by the addition of suitable perfumes, and the 
stickiness may be reduced by the admixture in reasonable 
proportions of the tallow and rosin base. Highly rosined 
soaps become very dark on aging. 

With rosin of the M and N grades of not more than 50 per 
cent, of the weight of stock, good laundry soaps of light 
color and excellent texture can be made by the method 
described later. These soaps are also free from sweating and 
rarely ever show any crystallization of salts on the surface. 

75. The best proportions of tallow and rosin to employ 
depend primarily on the firmness of the tallow; that is, on 
the percentage of stearin present. This proportion also 
changes with the season, less being used in summer than in 
winter. A soft tallow cannot assimilate so much rosin as a 
firm tallow and the desired firmness of the finished soap be 
obtained. 

It has been the custom of the trade to rate rosined soaps 
according to the proportion that the rosin bears to the fat 
stock by what is known as soapmakers’ percentage. A 
100-per-cent, rosin soap contains equal parts of tallow and 
rosin; a 50-per-cent, rosin soap contains 2 parts tallow and 
1 part rosin; a 150-per-cent, rosin soap contains 1 part tallow 
and 1.5 parts rosin. 

A soap properly made of these ingredients and in the pro¬ 
portion of 100 pounds of tallow and 50 pounds of rosin, with 
not more than 6 per cent, of soda-ash solution added in the 
crutcher, constitutes the standard high-grade settled rosin soap. 

76. Saponification of Olive, Red, Corn, and Cot¬ 
tonseed Oils. —Olive, red, corn, and cottonseed oils possess 


MANUFACTURE OF SOAP, PART 1 


61 


the same general chemical characteristics and behave in the 
same manner toward saponifying agents. 

Olive oil was originally the basis of the soap known to 
Americans as Castile soap and on the continent of Europe as 
Marseilles soap. Pure olive-oil soap is white and very mild 
in its detersive action. It is composed chiefly, if caustic 



soda is used to effect saponification, of sodium oleate. It is 
an excellent ingredient of a toilet-soap base and is especially 
adapted for use in the textile industry. 

Red oil, or commercial oleic acid, being a stronger acid 
than carbon dioxide, can be saponified to the extent of about 
90 per cent, with soda ash. Red-oil soap, sometimes called 
oleine soap, is practically identical in its composition and 

394—5 




























































62 


MANUFACTURE OF SOAP, PART 1 


properties with olive-oil soap, and is therefore equally adapted 
for the cleansing of textiles. 

Cottonseed-oil soap stock, when in a clean condition and 
as free as possible from coloring matter, is identical in com¬ 
position with red-oil soap and is adapted for the same technical 
uses. In connection with the use of cottonseed-oil soap stock, 
it should be remembered that it is simply soap, and unless in a 
very dehydrated condition does not admit of the yield common 
to all glyceride stock. It is simply an addition used because 
of its cheapness. 

77. Removal of Stock from Containers. —The stock 

is received in barrels, tierces, drums, hogsheads, pipes, or pun¬ 
cheons. In some cases, factories are located so that it can 
be handled in tank cars. A typical melting room, two views 
of which are shown by Fig. 8, is generally located on the first 
floor and directly over tanks which receive the melted stock. 
It is usually a room with the sides and floor sheathed with iron 
plates and provided with two or more compartments a and b 
so that one charge may be melting while another is being set. 

There is a track of inclined rails c in the center of each 
compartment on which the containers d easily roll. The 
gutter or pan e is placed directly beneath the container, and is 
also inclined in order that the melted stock will run forward and 
discharge to the pipe /which connects it with the stock tank g. 

The inlet of this pipe has a strainer to keep out the bungs 
and foreign material that would block the pipes and pump. 
The steam line h with valves and swing nipples i is laid in the 
center of the track at intervals to accommodate the different 
size containers. The steam-control valve j is located outside 
the compartment. 

When the charge has been set, blocked, and nipple adjusted 
to the bung of the container, the steam is turned on. In the 
case of fluid oils, it is not necessary to use any steam until all 
the fluid material has run out and then only for a short time. 
The length of time depends on the season. As the containers 
are removed they are examined with a light to make sure that 
they are empty. 


MANUFACTURE OF SOAP, PART 1 


63 


78. Storage Tanks. —The best arrangement of storage 
tanks is to have a sufficient number to take care of not only 
the different kinds of stock but of the different classes of each 
stored. This calls for an assortment of both large and small 
tanks. These tanks are provided with closed steam coils 
so as to keep the stock melted and in shape for pumping and 
gauges on the sides graduated usually in 1,000-lb. units. 

The stock received in the melting-out tank is allowed to 
settle. It is very necessary to store fats and oils as dry as 
possible to prevent decomposition. The 'melting-out tank is 
then emptied to the storage tank by a pump. The pump is 
fitted with a pet-cock by which samples can be drawn when 
the indicator on the tank shows the level at which water may 
be expected. As soon as water appears, the pump is shut off. 
This water is pumped to the first kettle taking a stock charge. 

It is good practice to connect all the drips from the storage- 
tank coils into a small tank and examine this tank for indica¬ 
tions of leaky coils. The tanks themselves will indicate leaky 
coils when they show more content on the gauge than the 
inventory carried on the tank. Once a week all the tanks should 
be tested for water and the stock kept dry. 

79. Piping. —One of the most important features about 
all piping in a soap factory is that all lines from tanks or 
kettles to pumps be equipped with steaming-out lines. The 
piping is so arranged with stop valves that live steam can be 
turned into them and the entire line of communication made 
clear before any transfer of material is attempted. It is also 
just as vital that as soon as any pump has delivered its final 
charge that the entire line be again steamed out both ways, 
that is from pump to kettle and from pump to tank before 
the valves are closed. 

It is not a rare thing to come into a soap factory on a morn¬ 
ing in winter and find lines blocked because of the failure to 
have the lines steamed out. This steaming-out applies to all 
lines carrying soap or lyes. 



























. 


























































MANUFACTURE OF SOAP 

Serial 2055B (PART 2) Edition 1 


PROCESSES OF SOAP MANUFACTURE 


GENERAL REMARKS 

1. The process of soap boiling- consists essentially of 
effecting a chemical reaction between a fatty body and a 
caustic alkali or between a fatty or resinous acid and a car¬ 
bonated alkali. The manner of bringing about this combina¬ 
tion and the conditions under which the reaction is completed 
give rise to three general classes of soap-manufacturing proc¬ 
esses, namely, boiled, semiboiled, and cold processes, whereby 
soaps, to which the same descriptive terms may be applied 
as well, are produced. 

Boiled soaps are also called settled soaps when in process of 
manufacture they have been subjected to changes by means 
of which the soap is purified and the glycerine separated. 

A semiboiled soap is one that has not been subjected to a 
graining process, but contains all the material added to the 
kettle. It is also called a run soap , which term, however, is 
without technical significance. 

A cold soap is one made by the direct combination of the 
materials in the proportions in which they are to remain in 
the finished soap, the combination being effected without 
the aid of heat other than that required to bring the ingre¬ 
dients to the requisite temperature and that evolved by the 
chemical reaction. 


COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED 




MANUFACTURE OF SOAP, PART 2 




The classification of processes just given is arbitrary and 
is not based on any essential chemical differences in the 
processes. The division is more mechanical than chemical 
and has reference chiefly to the time required, the artificial 
heat employed, and the mechanical apparatus necessary to a 
satisfactory operation of the process. 

The production of a good boil of soap is dependent entirely 
on the judgment used by the soap boiler. His operations are 
due to the knowledge that experience has taught him. The 
successful boilers are keen observers, and, outside of one 
chemical test for free alkalinity, they depend solely on the 
looks of the kettle as it is boiling. Some boilers become so 
expert that they can estimate quite closely the free alkalinity 
of stock changes by the taste. 


MANUFACTURE OF BOILED OR SETTLED SOAPS 


BOILING-ROOM PROCESSES 

2. Boiled Soaps. —The boiled soaps are the most impor¬ 
tant and constitute the class most generally manufactured 
and used. All laundry soaps, as well as the base for toilet 
soaps, are made by this process. 

Before discussing in detail the manufacture of soap of this 
class, the essential features of the process as it is continued 
throughout the time required for its completion will be con¬ 
sidered. There is arranged in Table I what may be called 
the outline of a boil of settled rosin soap. In this table is 
embodied an outline of the most important details of a boil 
of soap of this character. It is the soap most commonly made 
in the United States, and the procedure here outlined is the 
one generally followed. 

In an elaboration of the treatment given the soap in the 
kettle will be discussed the directions and precautions to be 
observed, from the addition of the soap stock and alkali to 
the kettle, through the various changes to the transferring 




OUTLINE OF A BOIL OF SETTLED ROSIN SOAP 


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4 


MANUFACTURE OF SOAP, PART 2 


of the product to the crutcher and the addition of filling 
agents, to its final treatment in the drying room and its 
preparation for shipment. 

3. The following soap-boiling process is carried out in 
factories where the maximum yield of glycerine is striven 
for. A yield of glycerine from 8 to 8^ per cent, is possible 
by following this method, when high-grade stock is used. 

First change: Into a kettle from which the niger of a pre¬ 
vious boil has been pumped on a second rosin change, run in 
water enough to cover 6 inches of the kettle bottom and boil 
with open steam. The stock pump is started and 18° Be. 
caustic-soda lye is added simultaneously. Where grease, tal¬ 
low, and oil are used, they are usually saponified in that order. 
When the saponification has started, noted by the swelling 
of the mass, the steam is eased off; only enough is used to 
keep the contents well mixed. This also serves to save room 
for the subsequent boiling. This change is complete when 
two boilings and tests show a free alkalinity of .20 per cent. 
Dry salt or brine is added until the soap becomes very open 
and the lye drops out clear. 

Second change: Every effort is made to remove all the 
possible glycerine before adding rosin because in the best 
practice no rosin lyes are sent to the glycerine plant. There¬ 
fore, a number of these wash changes are made. 

After the first lye has been drawn and sent to the glycerine- 
lye storage tanks, water and a small amount of 18° Be. caustic- 
soda lye are added to the kettle and the whole mass brought 
to a good vigorous boil with open steam. Water enough is 
used to close or flatten out the soap and enough caustic lye to 
hold the alkalinity up to .20 per cent. It is grained with salt 
like the first change and the lye drawn and disposed of as 
before. 

Third, fourth, and fifth changes: The number of these 
wash changes is dependent on the practice and experience of 
the individual plants. They depend also on the amount of 
water used on each change, the price of glycerine, the amount 
of exhaust steam available, the amount of glycerine-lye stor- 


MANUFACTURE OF SOAP, PART 2 


5 


age, and the capacity of the evaporators. The water used is 
usually expressed in terms of the stock and varies from 250 
to 450 per cent. A stock charge of 10,000 pounds will make a 
glycerine lye of 25,000 to 45,000 pounds. The procedure for 
these changes is the same as for the second change. 

First rosin change: When the last wash change has been 
drawn, scrap soap, a small amount of recovered salt (usually 
high in sulphate), and enough 25 to 30° Be. caustic-soda lye to 
open or grain the soap, is added. The alkalinity is kept up to 
2 to 3 per cent. A second rosin lye is pumped in while the 
rosin is being added and the kettle kept at a good boil. This 
change is grained on the caustic lye, and, after settling, the 
waste lye is drawn to an empty kettle and run to the sewer. 

Second rosin change: After the first rosin lye has been 
drawn off, enough caustic-soda lye of 25 to 30° Be. is added 
to bring the alkalinity up to 3 or 4 per cent. A boiled-up niger 
is pumped in and the contents of the kettle vigorously boiled. 

Strong change: When the second rosin lye has been drawn, 
open steam is turned on and enough water or 4-5° caustic- 
soda lye is added to flatten out the soap. When the mass is 
homogeneous and entirely flattened out, the steam is shut off 
and the kettle allowed to settle. 

Finish or settle: As soon as the strong change lye has been 
pumped off, the soap is boiled up and usually small amounts 
of water worked in with slow boiling. This is continued until 
the soap boiler is satisfied that the soap has all the character¬ 
istics needed. The steam is then shut off and the soap allowed 
to stand until ready to frame. 

4. Soap Kettle.—The soap kettle is made of steel plates 
of a thickness determined by its capacity. The plates are very 
carefully riveted and then calked to make them tight. Kettles 
are either square or rectangular; or cylindrical or slightly 
truncated. The first type is about 6 inches deeper in front 
than in back so as to provide a good pitch for draining, while 
the second type pitches to the center. Kettles of square or 
rectangular cross-section are more economical of space and 
make for a cleaner kettle room. It is necessary to brace the 



6 






































































MANUFACTURE OF SOAP, PART 2 


7 


square and rectangular types with cross-rods, while the cylin¬ 
drical types do not need them. For the manufacture of laundry 
soap alone, only open steam coils are provided. These coils 
are laid along the bottom. The steam header is extended 
down one corner of the kettle and the main arm is laid across 
to the other corner just off the bottom of the kettle, as shown 
in Fig. 1. This main arm has projecting arms of varying 
length which present a large heating surface. The arms have 
small holes drilled into them. 

5. The steam-control valve is in the main line at the top 
of the kettle, and between it and the soap line a small vent 
pipe with a valve is fitted. At about the usual niger level, an 
opening into the soap line is provided and on the inside of the 
kettle this opening is fitted with a swing joint and pipe that 
can be lowered as the soap is being withdrawn. 

On the boiling floor, the piping of each kettle is arranged 
for stock from the storage tanks, caustic-soda lye from the 
strong lye tank, steam, water and, a line by which lyes from 
any one kettle may be pumped into any other kettle. Con¬ 
nected to this line and also to the lowest part of the kettle 
there is a second line for drawing off the glycerine and rosin 
lyes. This line is also used for pumping nigers, strong change 
and second rosin lyes. 

6. During the boiling, but especially for the settling, it 
is important as well as economical to conserve all the heat. 
Therefore, all the kettles are heavily insulated on the sides up 
to the boiling-floor level. Usually this insulation consists of 
3 inches of magnesia-asbestos blocks wired on and covered 
with \ inch of asbestos cement. This is covered with canvas 
and painted. 

A very good layout ot kettles is one that provides for an 
empty kettle at all times, that is, one in which no soap is made. 
In large plants there is one of these kettles for every ten. 
Into this kettle all glycerine and rosin lyes are drawn, and by 
watching from the top, the valves on the soap kettle being 
emptied can be closed at the first sign of soap appearing in the 
kettle into which the glycerine lye is being run. The lye can 


8 


MANUFACTURE OF SOAP, PART 2 


then be sent to glycerine-lye storage tanks or in the case of 
rosin lyes direct to the sewer. If any soap has run in with 
the lye, it can be skimmed off and returned to the soap kettle. 
Fig. 2 shows the kettle-room arrangement, kettles, and piping 
plans. 

H. The arrangement of the steam piping in a round soap 
kettle is a very important matter, as the successful handling of 

the contents of the 
kettle depends a great 
deal on the shape, 
diamieter, and distri¬ 
bution of the coil. 
The diameter of the 
kettle will determine 
whether one or two 
open steam coils 
should be used. With 
a small kettle, one 
open steam coil or a 
crisscross jet in the 
center will suffice. 
This crisscross jet is 
.shown at /, Fig. 3. 
With a kettle from 15 
to 20 feet in diameter, 
a second open steam 
coil around the sides 
is necessary. The 
closed steam coil 
should completely 
cover the bottom of 
the kettle. Such a 
coil, with an open steam coil in the center, is shown in Fig. 4, 
in which a represents the central open steam coil, and b and c, 
respectively, the inlet and the outlet of the closed steam coil. 

8. The single pipe coil for closed steam, shown in Fig. 4, 
is more expensive than the jointed coil shown in Fig. 3, but 



Fig. 2 































































MANUFACTURE OF SOAP, PART 2 


9 


is not so liable to leak. The jointed steam coil is cheaper, 
more quickly and easily installed, and may be enlarged or 
repaired with only little trouble and expense. The only dis¬ 
advantage is the greater possibility of leakage, because of the 
numerous threaded joints. The valves on both the open and 
closed steam coils should be within easy reach of the soap 
boiler, in order that the boiling process will be under control 
at all times. 

9. The amount of stock that can be killed in a kettle of 
given capacity varies with the method of working. In general 



Fig. 3 


terms, it may be stated that 1 cubic foot of space is allowed 
for every 12 pounds of stock to be saponified, or for every 

100 pounds of stock. 



























































































































10 


MANUFACTURE OF SOAP, PART 2 


10. Saponification or Stock Change.— In this discussion 
the following combination of stock and rosin will be used: 


Stock and Rosin 

Ingredients 

Pounds 

Percentage 

Tallow . 

28,000 

90 

Cottonseed oil or grease. . . . 

3,000 

10 

Rosin, 36 bbl. 

15,500 

Percentage 
on Stock 

50 


This combination will produce an excellent laundry soap. 
However, the proportions and ingredients may be modified, 

depending on the quab 



Experience gained by working over the soap kettle is the 
final arbiter. The conscientious man will use the calculations 



















































MANUFACTURE OF SOAP, PART 2 


11 


of theory and supplement them with his practical knowledge. 
It is better to have a small quantity of unkilled stock on the 
stock change and the alkali completely absorbed than to have 
an excess of alkali wasted in the stock lye. 

12 . Stages of Saponification. —The saponification of 
glyceride stock requires three stages for the complete forma¬ 
tion of glycerine and the combination of the alkali with the 
fatty acids. While these stages do not admit of exact defi¬ 
nition in the soap kettle, they manifest themselves in certain 
characteristic conditions, which are familiar to every soap 
boiler, namely, the emulsion formed on admixture of stock 
and lye, the pasty mass obtained on continued boiling, and, 
lastly, the final condition resulting from boiling the pasty 
mass with an amount of alkali sufficient for complete sapon¬ 
ification. By means of chemical formulas, the three successive 
stages of saponification may be represented graphically: 

Raw Materials: 

Stearin (tallow), C 3 H^(C 18 H 35 0 2 ) 3 Caustic soda: 3 NaOH 

1. Emulsion, C 3 H 5 OH (C 18 H 35 0 2 ) 2 Soap: 3C ls H 35 0‘Na0 

Soap: C 18 H 35 0 • NaO 

2. Pasty mass, C 3 H 5 (OH) 2 (C 18 H 35 0 2 ) Caustic Soda: 2NaOH 

Soap: 2C 18 H 35 0 •NaO 

3. Glycerine, C 3 H 5 (OH) 3 Caustic Soda: NaOH 

The chief care is to add the stock and alkali simultaneously, 
with vigorous boiling, and in such proportions that, after 
saponification has started, the mass can be kept well open until 
the greater part of the alkali has been added. 

13. While the alkali and stock are being run in together, 
the mass in the kettle must be kept homogeneous by vigorous 
agitation or by boiling with live steam. Unless maintained 
in agitation, too little alkali is liable to cause bunching, by 
which is meant local saponification enclosing a mass of un¬ 
killed stock. Vigorous boiling will disintegrate and distribute 
this mass. An excess of alkali grains the mass, thus throw¬ 
ing it, as it were, out of solution, whereby combination is 
retarded. By the time the total amount of stock has been 


12 


MANUFACTURE OF SOAP, PART 2 


added, the greater part of the alkali should also be in the 
kettle, and boiling is continued, though less vigorously than 
at the beginning. 

14. Care should be taken to avoid an excess of alkali, 
and at the end of the change it should be added in small 
quantities only and not until the strength of the quantity pre¬ 
viously added has been absorbed. When the stock has been 
completely killed, the soap should slide freely from a paddle 
in large, transparent flakes. A small portion rubbed between 
the fingers should curl up smooth and dry and without any 
indication of grease. At this stage the contents of the kettle 
should boil smoothly, rising in the middle and descending at 
the sides, the appearance being very characteristic. 

On the completion of saponification, the contents of the 
kettle has become a clear, homogeneous mass, in which is 
present everything that was added during this stage, namely, 
soap, glycerine, water, and some sodium chloride, sodium 
sulphate, and sodium carbonate, which were introduced as 
impurities with the caustic-soda lye. In addition, the mass 
contains more or less mucilaginous or albuminous matter that 
was present as animal tissue in the stock. 

15. Testing for Free Alkalinity.—The free alkalinity of 

soap lyes is of the greatest importance. Every effort must be 
made to kill, or saponify, all the stock on the first change. It 
is just as important that the glycerine lyes be drawn as low 
in alkalinity as possible, because the more alkali they contain 
the more treatment they need before the evaporation can be 
started. A test for free alkalinity has been devised so simple 
that any man around the kettles can be taught its use in a 
short time. 

When the soap boiler is satisfied that the condition of the 
kettle warrants a test, a sample of soap is taken out with a 
long-handled can, while the soap is boiling toward the top of 
the kettle. Parts of this sample may come from different 
areas of the kettle, but the locality near the caustic-lye inlet 
must be avoided as there is generally a small drip there. The 
can used has a small hole punched in its side near the bottom. 


MANUFACTURE OF SOAP, PART 2 


13 


Dry salt enough to bring the sample to a good grain is stirred 
in. The can is kept tilted away from the hole. When it has 
stood long enough to drop a clear lye, the lye is drawn into a 
clean sample bottle by tilting in the opposite direction. The 
steam on the kettle is shut off while the test is being made. 


16. The cylinder used has special etchings on the side 
so that at the usual 10 c. c. mark, the word LYE is placed 
beside the mark. At a mark 20 c. c. farther up the word 
WATER is placed in a like manner. A mark is put for each 
2 c. c. and the half and full per cents, are etched on the sides. 
For all purposes a cylinder showing 4 per cent, alkalinity, 
will answer. The usual form of cylinder used 
is shown in Fig. 5. 

The test solution ^ sulphuric acid is made 

and standardized in the laboratory. A bottle 
of distilled water and an alcoholic solution of 
phenolphthalein is provided. The acid and dis- 
tilled-water bottles have quick-filling uncali¬ 
brated burettes for easy manipulation. 

The test is made by adding the sample of lye 
in the clean cylinder to the lye mark, a few 
drops of phenolphthalein and water to the 

water mark, and shaking to mix well. The — 

8 

sulphuric acid is then added until the color is 
discharged. 

The percentage of free alkalinity is then read directly on 

the cylinder. Each 2 c. c. of — acid used equals .10 per cent. 

8 



Fig. 5 


of free alkalinity. 

The steam is turned on and when the soap has boiled through 
completely for a few minutes, the test is repeated. If it holds 
the same alkalinity it is ready for graining. If not, a small 
quantity of 18° Be. caustic-soda lye is added and boiled 
through. This is repeated until the strength holds. By 
employing this easy test all guesswork in regard to free alka- 


394—6 





























14 


MANUFACTURE OF SOAP, PART 2 


Unity of lyes is removed. If the free alkalinity is too high, 
more stock is pumped in and killed. 

17. Graining the Soap.—The object of graining is to 
separate the soap from the glycerine. This is done by adding 
salt or strong brine. The soap is insoluble in this solution, and 
on account of its lower specific gravity rises to the top while 
the lye carrying the glycerine and nearly all the salt falls 
to the bottom. The kettle is properly grained when a good 
bright lye drops. There are other salts that will grain; caustic 
soda and sodium sulphate are among these. Caustic soda is 
used on rosin changes. Sodium sulphate does not grain as 
clear as sodium chloride and it requires much more of it. 
Where reclaimed salt is used, the amount of sodium sulphate 
formed by the treatment in the glycerine recovery becomes so 
troublesome that when it reaches 20 to 25 per cent, of the 
salt, it is used on a first rosin change, and is thus eliminated 
from the system when that lye is run to the sewer. 

Before adding the salt when graining, water enough is added 
to the kettle to make up the quantity of lye that it has been 
decided to make. This water is boiled into the soap. A good 
method of adding this water is to gauge it in time. The pres¬ 
sure from the city mains or from roof tanks that are held at a 
uniform level is constant enough for this. The instructions 
are usually given as 10 or 12 minutes of water. This is also 
done with caustic-lye solutions. 

18. An excessive quantity of water in the kettle mani¬ 
fests itself by frothing, and under such conditions dry salt 
must be used. The nature of the stock used should also be 
considered. Tallow alone forms a soap that, at this stage, 
is of a characteristically firm consistency, although fluid. 

Soaps made from cottonseed oil, red oil, olive oil, or rosin 
are very fluid, and from their consistency would seem to 
indicate the presence of an excessive quantity of water when 
such is not the case. Coconut oil makes a very fluid soap, 
and because of the large amount of salt required for graining, 
the latter should invariably be added in the dry state. 


MANUFACTURE OF SOAP, PART 2 


15 


19. With the contents of the kettle boiling quietly, dry 
salt or saturated brine is added in small quantities at a time 
and thoroughly boiled through the soap until a portion taken 
up on a paddle coagulates or separates so that waste lye runs 
from it. The waste should be clear, of salty taste, and should 
not contain free alkali in excess of two-tenths of 1 per cent. 
This amount of free alkali in waste-soap lye is not perceptible 
to the ordinary taste. 

The desired consistency of the grain is a condition arrived 
at by experience. The use of salt in excess of the amount 
required to produce this is not only wasteful, but also, if not 
thoroughly removed in the final settling change, tends to 
make the soap become fissured, or cracky, in the frames. The 
amount of salt added will partly determine the degree of 
hydration of the grained soap. 

The more concentrated the salt solution in contact with 
the soap, the less water will be retained by the soap. With 
an insufficient quantity of salt, the soap will not be withdrawn 
entirely from solution. With such a condition, the contents 
of the kettle on cooling will not present a clean line of 
demarcation between the soap and the under lye, but there 
will be an intermediate zone of soft soap. Waste lye with¬ 
drawn hot from soap that has been insufficiently grained, 
will, on cooling, have the consistency of soft soap. 

20. In boiling soap of the character under discussion the 
stock lye should not have a greater density than 13° Baume, 
and will contain from 7 to 10 per cent, of salt. The soap is 
sufficiently grained when a waste lye of this character is with¬ 
drawn. It has been found by analysis that this is the lowest 
density that will remove the soap completely from solution; 
more salt than this is unnecessary and wasteful. The stock 
lye is the clearest and least discolored, and, owing to the high 
percentage of glycerine present, is the most valuable. 

21. With the first appearance of a tendency to grain, the 
quantity of salt added previously should be thoroughly boiled 
through the soap, and each subsequent addition should be 
boiled through in the same manner before more is added. 


16 


MANUFACTURE OF SOAP, PART 2 


When the desired grain has been obtained, the soap is boiled 
up to the top of the kettle, and the steam is turned off. 

The time allowed for settling after graining depends on how 
fast the kettles must be worked toward the finish. Usually 
the kettle is rosined the first or second day after the stock 
change. This allows at least one glycerine lye to stand over¬ 
night. The other glycerine lyes may be drawn 2 hours after 
the graining is completed. 

22 . First Rosin Change.—A pure tallow soap has such 
poor lathering qualities that it needs rosin or oil to make it 
more soluble. Rosin and oil are used in laundry soap, but 
oil only, in toilet soap. The rosin is added either directly to 
the kettle or is saponified alone in another kettle and pumped 
in. Where the rosin is added directly, the barrels are generally 
rolled up to the kettle previous to the change being started and 
all the iron bands but one cut and removed. This is done so 
that by cutting the last band, the staves and heads fall apart 
and much time is saved. The rosin is broken into small pieces 
and shoveled into the kettle. 

It is cheaper to use soda ash than caustic for this sapon¬ 
ification. A 12° Be. soda-ash solution is made and brought 
to a boil, the rosin is shoveled in as in a direct saponification 
and the whole mass kept boiling until no lumps of rosin are 
seen on the surface when the steam is shut off. Just before 
pumping, some dry salt is added to make it pump better. With 
the use of saponified rosin much less caustic lye is needed for 
this change. One thousand pounds of rosin requires about 
150 pounds of soda ash. 

A second rosin lye is pumped in on this change so that the 
excess of caustic that it contains can be used in dissolving the 
rosin and also to purify the soap by washing out the color and 
soluble impurities. The rosin changes are kept well open with 
caustic as very little salt is used. It is boiled thoroughly and 
always stands overnight so as to get out all the impurities 
possible. 

23. Second Rosin Change.—The main object of the sec¬ 
ond rosin change is to insure complete saponification. The 


MANUFACTURE OF SOAP, PART 2 


17 


boiled-up niger is added to fill up the kettle and reclaim all 
the good soap possible. All rosin changes are very tricky in 
their boiling and require all the skill of the soap boiler in 
getting a good mixing of all the ingredients. The steam is put 
on for a short while and the kettle watched very closely. The 
steam has a tendency to hold in pockets and break through 
with such violence as to jump out of the kettle. By putting 
on and shutting off the steam until it begins to break through 
quietly, a gentle boil may be had. 

On the addition of alkali, as previously noted, the soap is 
well boiled through simultaneously with the addition of the 
rosin. Combination ensues quickly. The same care should 
be taken to insure the fullest absorption of the alkali, with 
the least amount added in excess to be discharged into the 
rosin lye. 

During this change, combination is greatly assisted by keep¬ 
ing the contents of the kettle in a state of partial precipitation 
by the addition of caustic-soda lye. In the language of the 
soap boiler, this is termed either graining the soap with alkali, 
so called from the consistency that the soap assumes, or keep¬ 
ing the soap open on alkali, by which is meant not allowing 
the soap to close or flatten, or to lose its grainy appearance 
on passing into complete solution. Opening the soap, there¬ 
fore, means partly precipitating it by the addition of a body 
in whose solution it is insoluble. 

24. The rosin lye is nearly always very highly colored, 
with a depth of color depending largely on the quality of the 
rosin used. On the stock change, 31,000 pounds of mixed 
stock was killed. This admixture will carry well one-half 
its weight, or 15,500 pounds, of rosin—roughly, 36 barrels. 
After the withdrawal of the rosin lye there will remain in the 
kettle about 70,000 pounds of soap. 

25. Strong Change.—The strong change is boiled on 
water if there is enough alkali left from the second rosin 
change, or with 4° to 5° Be. caustic lye if it appears weak. 
The soap which has flattened out with the water will open 
very slightly so as to drop only a small quantity of slimy lye. 


18 


MANUFACTURE OF SOAP, PART 2 


This change is boiled slowly, which tends to make the contents 
of the kettle homogeneous. 

26. The purpose of the strengthening change is to com¬ 
plete the saponification and to discharge the salt, coloring 
matter, and other impurities retained mechanically by the soap. 
No salt is used for graining on this change. The 2 to 4 per 
cent, of salt commonly present in strengthening lyes represents 
the amount that has been retained mechanically by the soap 
and washed from it on this change. 

The alkali wash promotes the discharge of the coloring 
matter, and completing the saponification of the last traces 
of unkilled stock also assists very materially in the develop¬ 
ment of the texture desired in the finished product. 

27. Settling the Soap .—Finishing or settling the soap 
consists essentially in thinning the soap to the desired con¬ 
sistency with either weak lye or water. The water may be 
added during boiling or it may be derived from the steam 
condensed during this change. The strengthening lye from the 
preceding change is withdrawn and the soap is boiled up with 
live steam. Water is added in small quantities at a time 
until the soap is closed. 

The boiling on the settle is done very slowly and may take 
all day to bring it into a condition that satisfies the soap 
boiler. Good soap can never be harmed by too much proper 
boiling. 

Some free alkali is retained mechanically by the soap after 
the withdrawal of the strengthening lye. This amount is 
sufficient to impart a slight sharpness or alkalinity to the 
settled soap. It is claimed by some manufacturers that the 
soap should be settled in a perfectly neutral condition; others 
claim that the best results are obtained with a slight sharpness 
present. 


28. The soap is boiled up to the top of the kettle and is 
then allowed to stand for about 6 or 7 days, during which time 
the contents of the kettle, by virtue of the different specific 
gravities, resolves itself roughly into two portions, namely, 


MANUFACTURE OF SOAP, PART 2 


19 


the finished soap, carrying about 30 per cent, of water (this 
proportion, however, varying with the grain of the finish), 


TABLE II 

ANALYSIS OF SOAP DURING SETTLING PERIOD 



When Steam 
is Shut Off 

Per Cent. 

After 12 
Hours 

Per Cent. 

After 60 
Hours 

Per Cent. 

Free NaOH . 

.15 

.02 

Trace 

Free Na o C0 3 . 

.22 

.13 

.11 

Salt. 

2.54 

.77 

.40 

Water . 

45.58 

32.82 

30.40 


and the niger, which carries considerably more water than 
does the supernatant soap, as well as the impurities and 
coloring matter settled from the latter. The settling change is 
a very important one, for on its proper operation depends the 
success or failure of the boil of soap. The length of time 
allowed to settle a boil, varies. It is best when permitted 
to stand a week. Plowever, in the busy seasons it can be 


TABLE III 

ANALYSES OF NIGERS OF SETTLED ROSIN SOAP 



1 

2 

3 

Water . 

59.14 

66.29 

55.86 

Fatty and rosin an¬ 
hydrides . 

30.41 

23.27 

35.83 

Combined alkali.... 

3.92 

3.16 

4.36 

Free NaOH . 

.70 

1.02 

.86 

Free Na,CO s . 

.56 

.56 

.58 

Salt . 

2.34 

3.24 

1.71 

Undetermined . 

2.93 

2.46 

.80 


100.00 

100.00 

100.00 


crutched and framed on 4 or 5 days’ settling. 1 he settles of 
the same day are usually framed in the order of their temper- 












































20 


MANUFACTURE OF SOAP, PART 2 


atures, the coolest one being taken first. If one a day earlier 
than its schedule is needed, the coolest one is also framed 
first. 


29. Niger .—The liquor from the settled soap is called 
the niger. It contains the impurities and constitutes from 20 
to 25 per cent, of the volume of settled soap in the kettle. 
This proportion varies with the degree of hydration of the 
finished soap, the length of time allowed for settling, and 
the temperature of the mass. Analyses of the principal com¬ 
ponents of typical nigers are given in Tables III and IV. 

The more thinly the soap is finished, the larger will be the 
niger, and the impurities of the finished soap, other things 

being equal, will be more 
completely settled into it. 
Care should be taken not 
to finish the soap too 
thinly, for the excessive 
quantity of water added to 
the kettle not only makes 
the finished soap softer, 
but leaves a large bulk of 
niger to receive subse¬ 
quent treatment. 

30. On the other 
hand, a soap finished too 
closely, owing to the addi¬ 
tion of an insufficient quantity of water, will separate the 
impurities very incompletely and yield a small niger. Other 
conditions being satisfactory, the longer the settling period, the 
more complete will be the separation of impurities, with the 
formation of a niger of proper volume. If, during this period 
great attention is not given and the soap is allowed to cool too 
quickly, which is often the case with a small kettle or with one 
exposed to the weather, especially in winter, separation of the 
impurities will be checked by a local or general cooling of the 
mass, and the niger will remain distributed unequally through¬ 
out the soap. This is overcome by insulating the kettle. 


TABLE IV 

ANALYSIS OF NIGER OF A TOILET 

SOAP 


Water. 

70.83 

Fatty anhydrides! 
Combined alkali J 

22.65 

Free NaOH . 

.78 

Free Na 2 CO B . 

.80 

Salt . 

3.76 

Undetermined. 

1.18 


100.00 














MANUFACTURE OF SOAP, PART 2 


21 


31. The settling change is not primarily a purifying 
change, but provides first for the production of a mass of a 
certain appearance and consistency, and when this is obtained 
and the proper conditions just noted are observed, the soap 
mass separates the impurities, thus forming the niger. 

The soap mass is said to be finished fine or coarse, or, 
respectively, hard or soft, according to its degree of hydration. 
The condition described as fine or hard obtains when the 
soap taken up on the paddle and held in a slanting position 
falls from it in short, small flakes and cools rather quickly. 
The condition described as coarse or soft obtains when the 
soap falls from the paddle in large flakes and cools less 
quickly. The appearance and consistency must be learned by 
actual experience, by personal handling of the material itself. 
The process of clarification can be noted on the top of the 
kettle as soon as the final steam is shut off. 

32. Filling of Soap .—The detergent qualities of soap are 
greatly increased by the addition of certain substances in 
aqueous solution while the soap is in a fluid state. 

Borax and sodium carbonate are employed, but the use of 
the former for this purpose is, as a rule, displaced by the 
cheaper alkaline carbonate. 

As all surface water contains mineral salts, chiefly the 
carbonates and sulphates of lime and magnesium, it is neces¬ 
sary to neutralize these before the soap can exert any cleansing 
action. Insoluble soaps of lime and magnesium are formed 
by the combination of soluble soaps and the salts just men¬ 
tioned, which impart the so-called hardness to surface water. 

Sodium carbonate is a valuable addition to a soap, as a 
more economical use of soap is effected by its incorporation, 
as will be described subsequently. The carbonate effects the 
neutralization of mineral salts, thus leaving the soap to exert 
its legitimate cleansing action. The value of sodium carbonate 
to increase the detergence of soap was early recognized, as 
was also its property of hardening the soap, thus permitting 
the incorporation of more water than would be possible 
without its use. 


22 MANUFACTURE OF SOAP, PART 2 

Sodium silicate lends itself readily to incorporation with 
fluid soap, as it possesses very little detergent power. It is 
primarily a cheapener and imparts a smooth appearance to 
the finished soap, which becomes extremely hard on drying. 

33. Sodium carbonate and sodium silicate are the chief 
filling agents. Their use in soap in large or small amounts 
is determined by the grade desired to be made and gives rise, 
respectively, to the terms heavily filled and lightly filed. 

Mineral soap stock is a residuum from petroleum distillation 
that is frequently used in heavily filled soap. This stock 



imparts a smooth appearance to such soap, and thus counter¬ 
acts the tendency of the mineral salts mentioned to grain the 
soap when added in large amount. 

The limit to the use of filling agents is determined by the 
intelligence of the consumer. The incorporation in soap of 
filling agents is not, strictly speaking, an adulteration, so 











































































MANUFACTURE OF SOAP, PART 2 23 

long as the product is sold at a price commensurate with its 
quality. 

34. Crutching the Soap.—For the incorporation of filling 
material into soap, the belt-driven crutcher is generally 
employed. There are three styles of this machine, each of 
which possesses several points of excellence. 

Style A, shown in Fig. 6, consists of a cylindrical vessel a, 
in which is mounted a vertical shaft carrying a series of hori¬ 
zontal paddles b. These paddles rotate entirely within the body 



Fig. 7 

of the soap, which remains practically stationary. The blades 
of the horizontal paddles may be so constructed, however, 
as to impart an upward movement to the soap. With a 
crutcher constructed as shown in Fig. 6, it is impossible to 
incorporate air into the mass of soap, as the mixing is done 
entirely within the body of the soap. 

35. The distinguishing feature of the crutcher known as 
style B, shown in Fig. 7, is an inner concentric cylinder a, 
enclosing a broad Archimedean screw d mounted on a vertical 
shaft. Both the outer shell e and the concentric cylinder a 





























































































































































24 


MANUFACTURE OF SOAP, PART 2 


may be steam-jacketed or water-jacketed or fitted for both. 
This style is more commonly used without the steam jacket. 

With this crutcher, the entire mass of soap may be moved 
from below upwards through the central cylinder by means 
of the screw d, and downwards between the outer shell e and 
the concentric cylinder a, or in the reverse direction, according 
as the belt is advanced or reversed. 


36. Style C, shown in Fig. 8, is essentially the same as 
style A. The shaft of this crutcher is horizontal, with blades 



Fig. 8 


of even or varying length mounted in screw-like fashion on it. 
Soap is pumped or dropped into the hopper a until the 
paddles c are covered to a depth of 2 inches. The crutcher 
is then started and run until the soap is crutched. The screw¬ 
like motion of the paddles works the contents of the crutcher 
toward the outlet b, which is closed by the counterpoise d. If 
the soap is not too thick, it will flow freely from the outlet b. 
If too thick, it is necessary to start the crutcher. 





























































































































































































































































































































MANUFACTURE OF SOAP, PART 2 


25 


Each type of crutcher may be steam-jacketed or water- 
jacketed or both if desired. In factories that are not equipped 
with a separate remelter, this feature is essential. The steam- 
jacketed crutcher can then serve as a remelter. The capacity 




of a crutcher is that of one frame, namely, 1,200 pounds. 
The crutchers are sometimes hung between floors in a cage 
or pit. It is the general practice to decide on a set temperature 
at which to drop each frame of the same class. A temperature 
of 142° to 145° F. is very good for the soap just described. 
















































































































26 


MANUFACTURE OF SOAP, PART 2 


37. The use of the remelter is gradually growing less. 
It is much easier and cheaper to arrange the crutchers as 
shown in Fig. 9. This allows all clean scrap from the cutting 
tables to be added to the fresh soap going to the crutcher, 
where it serves a two-fold object. First, it is worked back 
into a finished form; and second, it cools the hot soap to the 
desired temperature. With well-insulated kettles, the soap 
crutching is seldom under 160° F. in winter and 170° to 185° F. 
in summer, and its temperature can be entirely controlled by 
the use of scrap so that water in the jackets is seldom used to 


get the temperature 
desired before drop¬ 
ping. 



Soap is pumped to 
the box, which is 
fitted with a heavy 
strainer, usually a 
wire basket. The 
amount of scrap that 
experience has deter¬ 
mined to be proper, 
is added to the hot 
soap and stirred in 
with a paddle. As 
most of this scrap 
comes fresh from the 
slabber and cutting 


Fig. 10 


tables, it softens quickly. When the charge has been taken into 
the crutcher, the crutching is continued until the whole mass 
is homogeneous and shows no signs of the scrap soap used. 
It takes 10 to 12 minutes to accomplish this. This work pro¬ 
ceeds so regularly that it is usually controlled by the clock. 

38. Floating Soap.—With all other classes of soap, the 
crutcher is always filled well above the paddles or blades to 
exclude carefully all air. It is desirous to make ordinary 
laundry soap as dense in structure as possible. In making 
floating soap, however, this procedure is reversed and the 









MANUFACTURE OF SOAP, PART 2 27 

» 

specific gravity is lowered by the incorporation of minute air 
bubbles. 

To accomplish this, the crutcher is filled to within 6 to 10 
inches of the top and covered, and the crutching continued 
until the soap has swollen to some predetermined height. 

39. Soap Pumps.—T he liquid soap is transferred to the 
crutcher by means of a pump. The pumps used vary some- 





Fig. 11 

what in construction, and only those most generally used will 
be described. 

In the Tabor rotary pump, the working parts of which are 
shown in Fig. 10, a is the shell, or case, of the pump; b is the 
head that covers the end of the shell; c is the piston that 
carries the valves; d are the valves that pass through the piston 
in the ways e, and as the piston revolves, they pass in and out, 
back and forth through.the piston, following the inside lines 
of the shell. The piston sets tightly against the shell at the 












































28 


MANUFACTURE OF SOAP, PART 2 


point f, between the point of suction and discharge. Rotating 
the piston creates a vacuum in the suction pipe, and the pump 
is thus set into operation. 

40. The Hersey rotary pump, shown in Fig. 11, consists 
essentially of a cone-shaped casting, or piston, d, carrying 
blades, the whole being mounted on the end of a shaft e. 
The piston rotates in a specially shaped case, and when it 
turns in the direction indicated by the arrow, suction takes 
place at the orifice a and discharge at e. The reverse occurs 
when the piston is rotated in the opposite direction. 

41 . The Johnson rotary pump, shown in Fig. 12, consists 
of an outside shell a, with suitable parts b and c for connecting 



suction and discharge pipes; two side plates, one of which 
is shown at d, with the cam g, and inside of all a circular 
casting, or piston, e, in which are held the piston heads / 
operated by the cam g. As the piston revolves, the cam g 
causes the piston heads f to move in and out of their ways, 
being at their extreme positions as shown in the figure. The 
block h separates the suction and discharge chambers. 

42. The rotary type of pump is adapted for a variety of 
uses in the soap factory. Its simple construction, ease of 






























































































































































MANUFACTURE OF SOAP, PART 2 


29 


operation, and freedom from expensive repairs give it many 
advantages over the ordinary steam pump. The chief uses 
for a pump are to transfer stock and caustic lye to the soap 
kettle, the finished soap to the crutcher, and waste-soap lye 
to the glycerine refinery. Large plants are usually laid out 
so that as much work as possible can be done by gravity. As 
a rule, all glycerine lyes, caustic-soda lyes, and sal-soda 
solutions are handled in this manner. 

43. On the discharge side of the pump there should be 
connected a steam pipe that will serve to blow out and clean 
the interior of the pump and the discharge pipe after use. 
As shown in Figs. 10 and 11 the pumps are provided with 
tight and loose pulleys, on the latter of which the belt may 
be shifted when the pump is not in use. 

For pumping the soap from the kettle to the crutcher, the 
pump should be placed below the level of the draw-off pipe 
in the kettle, and the outlet, or discharge, pipe should be of 
slightly smaller diameter than the intake pipe. In this way 
gravity will aid the feed and provide for a steady discharge. 
The rotary, belt-driven pump represents a great improvement 
in productive economy over the old-time ladle and bucket as an 
instrument for transferring soap from vessel to vessel. 


FILLINO MATERIALS 

44. Soda Ash.—The most valuable material to be added 
to laundry soap is soda ash. This material is introduced into 
the crutcher in the form of a saturated solution. The crutcher 
room is usually provided with a steam-heated kettle having an 
agitator for dissolving the soda ash as required. During the 
afternoon of the day previous to crutching, a quantity of 
solution sufficient for the entire boil of soap is made up. 

When the arrangement of the factory permits, the sal-soda 
boiling tank is placed beside the caustic-soda lye tank on the 
soap-boiling floor. Another small tank is put on the crutching 
floor into which the sal-soda solution is drawn for use as 
needed. This serves to hold as much heat as possible in the 

394 —=•!* 



30 


MANUFACTURE OF SOAP, PART 2 


main solution. The amount of sal-soda solution is usually 
weighed for each crutcher charge of soap. 

45. With a soda-ash kettle of given capacity, the quantity 
of soda ash and water necessary to produce a solution of the 
required density is easily ascertained by experience. The mix¬ 
ture is boiled with open steam to a density of 33° Baume 
while hot. During the night the impurities in the solution, 
introduced by the soda ash, will have settled to the bottom and 
the solution will have cooled to a temperature of about 140° F., 
with the specific gravity increased to 36° Baume. A solution 
lower than this in specific gravity should not be used in filling 
a soap. 

The draw-off pipe should be placed 2 or 3 inches above the 
bottom of the sal-soda kettle, so as to avoid the removal of 
the settled impurities. 

46. The quantitative properties of sodium-carbonate 
solutions above a density of 18° Baume are determined at a 
temperature of 30° C. At a temperature of 15° C., solutions 
of the density shown in Table V (B) will crystallize, forming 
the hydrated salt, Na 2 CO z '\OH 2 0, or Na 2 CO z 10Aq (Aq. is 
the abbreviation for the word aqua, meaning water) as it 
is more frequently written, commonly known as sal-soda. 

47. Concentrated solutions of sodium carbonate, when 
added in large amounts to any soap and particularly to soap 
made from soft stock, which, as known, sweats more readily 
than soap made from firmer stock, will soon cause the soap 
to effloresce. This is a most disagreeable property and detracts 
greatly from the appearance of the product. Also, when 
added in greater quantity than the soap can assimilate, the 
soda ash tends to grain the soap. With heavily filled cheap 
soaps, this condition represents the limit of the addition; soda 
ash and other filling agents possessing detergent properties 
then become adulterants. 

48. Borax.—The addition of borax to soap is desirable, 
as this material is a mild alkali and possesses all the advantages 
of soda ash with none of its caustic properties. Owing to the 


TABLE V 


SPECIFIC GRAVITIES OF SOLUTIONS OF SODIUM 
CARBONATE (LUNGE). (A) AT 15° C. 


Specific 

Gravity 

Degrees 

Baume 

Degrees 

Twaddell 

Per Cent. 
N (Z2CO3 

Per Cent. 
Na 2 COz 

10 Aq. 

1 C. M. Contains Kg. 

Na^COz 

NozCOz 

10 Aq. 

1.007 

1 

1.4 

0.67 

1.807 

6.8 

18.2 

1.014 

2 

2.8 

1.33 

3.587 

13.5 

36.4 

1,022 

3 

4.4 

2.09 

5.637 

21.4 

57.6 

1.029 

4 

5.8 

2.76 

7.444 

28.4 

76.6 

1.036 

5 

7.2 

3.43 

9.251 

35.5 

95.8 

1.045 

6 

9.0 

4.29 

11.570 

44.8 

120.9 

1.052 

7 

10.4 

4.94 

13.323 

52.0 

140.2 

1.060 

. 8 

12.0 

5.71 

15.400 

60.5 

163.2 

1.067 

9 

13.4 

6.37 

17.180 

68.0 

183.3 

1.075 

10 

15.0 

7.12 

19.203 

76.5 

206.4 

1.083 

11 

16.6 

7.88 

21.252 

85.3 

230.2 

1.091 

12 

18.2 

8.62 

23.248 

94.0 

253.6 

1.100 

13 

20.0 

9.43 

25.432 

103.7 

279.8 

1.108 

14 

21.6 

10.19 

27.482 

112.9 

304.5 

1.116 

15 

23.2 

10.95 

29.532 

122.2 

329.6 

1.125 

16 

25.0 

11.81 

31.851 

132.9 

358.3 

1.134 

17 

26.8 

12.61 

34.009 

143.0 

385.7 


(B) AT 30° C. 


Specific 

Gravity 

Degrees 

Baume 

Per Cent. 
Na 2 C O 3 

Per Cent. 
NchCOz 

10 Aq. 

1 Liter Contains Grams 

Na^COz 

Na 2 COz 

10 Aq. 

1.308 

34 

27.97 

75.48 

365.9 

987.4 

1.297 

33 

27.06 

73.02 

351.0 

947.1 

1.285 

32 

26.04 

70.28 

334.6 

902.8 

1.274 

31 

25.11 

67.76 

319.9 

863.2 

1.263 

30 

24.18 

65.24 

305.4 

824.1 

1.252 

29 

23.25 

62.73 

291.1 

785.4 

1.241 

28 

22.29 

60.15 

276.6 

746.3 

1.231 

27 

21.42 

57.80 

263.7 

711.5 

1.220 

26 

20.47 

55.29 

249.7 

673.8 

1.210 

25 

19.61 

52.91 

237.3 

640.3 

1.200 

24 

18.76 

50.62 

225.1 

607.4 

1.190 

23 

17.90 

48.31 

214.0 

577.5 

1.180 

22 

17.04 

45.97 

201.1 

542.6 

1.171 

21 

16.27 

43.89 

190.5 

514.0 

1.162 

20 

15.49 

41.79 

180.0 

485.7 

1.152 

19 

14.64 

39.51 

168.7 

455.2 

1.142 

18 

13.79 

37.21 

157.5 

425.0 


31 





































32 


MANUFACTURE OF SOAP, PART 2 


higher cost, its use in soap manufacture is limited; with 
certain brands, only sufficient is used to justify in a measure 
the title given to the soap. 

49. Sodium Silicate.—Next to soda ash, sodium silicate, 

commonly called water glass or soluble glass, is the most 
extensively used filling agent. Its consistency lends itself to 
ready incorporation with the semifluid soap. It possesses 
detergent power, and when used with due regard to the price 
of the finished soap, it is a valuable addition to the ordinary 
household soap. 

Sodium silicate is made by fusing pure white sand and soda 
ash in a reverberatory furnace, such proportions being used 
that the resulting glass can be expressed by the formula 
Na 2 0 ‘4Si0 2 . The resulting glass is broken into fragments 
and introduced into a digester that is already charged with 
an amount of water to yield a solution of any density desired, 
and high-pressure steam is then admitted. When solution 
is complete, the contents of the digester is run into barrels, 
in which shape it is received by the soap maker. 

50. Sodium silicate is generally used at a density of 
40° Baume, in which condition it has the consistency of thick 
molasses, is transparent, and hardens quickly on exposure. At 
ordinary temperatures it will flow readily from the barrel. It 
must be in a fluid condition when used. In cold weather it 
may be softened by blowing steam into the barrel. If the 
head of the barrel is removed and the contents exposed to 
the air, those varieties deficient in alkaline strength will 
jelly, or separate free silicic acid through the displacement 
of the latter acid by the stronger carbonic acid of the atmos¬ 
phere. This may be overcome by stirring up the mass with 
strong caustic-soda lye, thus effecting a combination of the 
silicic acid with alkali. 

51. When intended for the use of soap makers, the 
sodium silicate has an average composition as follows: 
Water, 62.8 per cent.; Si0 2 , 28.7 per cent.; Na 2 0, 8.5 per 
cent. The more silicic acid the product contains, the more 
difficult it will be to dissolve it in water. The composition 


MANUFACTURE OF SOAP, PART 2 


33 


of commercial sodium silicate, as it occurs in solutions of dif¬ 
ferent densities to be used for different purposes, is variable, 
depending on the proportions of soda ash and silica used 
in the original charge and on the amount of water in which 
the fused mass is dissolved in the digester. There is practically 
no neutral silicate; that which is called neutral contains an 
excess of silicic acid, although it is not acid to litmus. 

52. On aging, soap filled with sodium silicate becomes 
very hard. When well mixed with the soap, a reasonable 
proportion of sodium silicate greatly improves the appear¬ 
ance and enables a larger quantity of sal-soda to be carried 
without the efflorescence that would soon be produced with¬ 
out its use. 

While sodium silicate possesses detergent properties, it is 
used primarily as a cheapener. By the use of suitable pro¬ 
portions of solutions of soda ash and sodium silicate, the 
quality of laundry soap is greatly improved. The soap is 
made more durable from the hardness produced by the 
crystallization of the salts; also the rapid drying of the soap 
is retarded. 

When used in excess in cheap soap, the salts not only per¬ 
mit the absorption of a larger amount of water than would 
otherwise be practicable, but also, when used in soap made 
from soft stock, they impart a firmness that, without their 
use, would not be possible without having previously trans¬ 
formed the product into a variety of boiled-down soaps. 

53. Miscellaneous Fillers and Adulterants.—Ground 
quartz, or silica, marble dust, mineral soap stock, a petroleum 
residuum, starch, and talc may be mentioned as fillers. They 
are adulterants pure and simple. 

54. Perfuming the Soap.—With the best grades of 
laundry soap, it is common practice to add a small amount 
of either a single essential oil or a mixture of oils in order 
to produce a pleasant and lasting perfume. The quantity 
added is seldom in excess of 2\ pounds per frame. The 
selection of the oil or mixture of oils is best determined by 
experiment, the object being to choose an oil or mixture 


34 


MANUFACTURE OF SOAP, PART 2 


of oils that will best counteract the resinous odor inseparable 
from rosined soaps. Too much care cannot be used in select¬ 
ing a perfume for a soap, because, in many cases, the users 
identify the soap by its perfume. 

55. Crutching the Filler and Perfume Into the Soap. 

The temperature best adapted to crutching depends largely on 
the character of the stock used in the soap and on the quantity 
and temperature of the filling material added in the crutcher. 
The temperature of crutching need not be so high for soap 
made from soft stock, because of its natural softness, as 
for soap made from firm stock. 

If the crutcher is provided with a steam jacket, the soap 
can be easily kept at any desired temperature. Such devices, 
however, entail the use of a large amount of steam, and, 
moreover, for this purpose are not absolutely essential, but 
desirable. It is best and of great advantage to add the soda-ash 
solution at the same temperature as that of the soap, and 
when prepared as has been previously explained, it will be at 
the proper temperature when the soap is ready to crutch. 

56. When ready to crutch, the swing-joint pipe is lowered 
a short distance below the level of the soap in the kettle and 
held in place by a chain, as shown in Figs. 3 and 4. The 
rotary pump is started and the crutcher is filled. When 
approaching the line at which the niger usually shows, the 
swing joint is watched very carefully and lowered a little 
at a time, just enough to keep the pump from sucking air. 

The speed of crutching is best determined by experience. 
For a soap of the character under discussion, 80 pounds 
of sal-soda is run in and the mass crutched until fairy homo¬ 
geneous. The sodium silicate is then added and crutched in. 
The perfume is added last, about 2 minutes before dropping, 
so as to avoid loss from the hot soap, and the soap is crutched 
until a portion removed on a paddle is perfectly homogeneous 
in texture and smooth in appearance. 

Under satisfactory conditions, from 10 to 12 minutes is 
sufficient to crutch a frame of soap. With completely 
saponified soap that is pumped into the crutcher at a temper- 


MANUFACTURE OF SOAP, PART 2 


35 


ature not exceeding 160° F. in winter and that carries a 
reasonable amount of filling, no trouble need be experienced 
in crutching. The primary conditions for satisfactory work 
are that the stock shall be completely saponified and the soap 
well settled. As to the soap being neutral or having a slight 
sharpness, there is a difference of opinion. 

57. At the end of the crutching period, the outlet in the 
bottom of the crutcher is opened and the contents is emptied 
into a frame standing on the floor immediately below the 
crutcher. Where it is possible to operate two crutchers, 



Fig. 13 


mounted as shown in Fig. 13, the work is greatly facilitated, 
as the crutching can proceed in one while the other is being 
emptied, and vice versa. The man in charge of crutchers can 
always tell when the niger is reached. The appearance of the 
soap changes very decidedly; it becomes dark, thin, and streaky. 
By allowing it to flow across a trowel or paddle, the change 
is caught almost at once. The pump is shut off and the niger 
in the pump and line steamed back into the kettle. The niger 
is boiled up and pumped into any waiting second rosin change. 
The kettle is then ready for a fresh charge of stock. 































































































































































































36 


MANUFACTURE OF SOAP, PART 2 


FINISHING-ROOM PROCESSES 

58. Framing the Soap.—The soap frame, shown in 
Fig. 14, has attained its present shape and size as the result 
of experience in handling soap at this stage of its manufac¬ 
ture. This frame consists essentially of an uncovered box 
with removable wood or sheet-steel sides, and with ends of 
wood or sheet steel set on a wooden bottom, which is mounted 
on truck wheels. It has a capacity of 1,000 to 1,200 pounds. 

There are various styles manufactured, all with the single 
aim of producing a box that can be readily put together and 
taken apart, that will be durable, as light in weight as is 



consistent with strength, that can be easily moved about, and 
that will possess the most important qualification—tightness. 
The dimensions of the frame are variable and are determined, 
especially the width, by the size of the bar into which the 
slabbed soap is to be cut, it being the aim to keep the per¬ 
centage of scrap at the cutting table as low as possible. 

In the frame-room equipment, it is best to have an extra 
bottom for each frame. The sides of a frame may be removed 
after the soap has cooled sufficiently to permit this, and then 
mounted on the extra bottom. This is a most economical 
method, the usefulness of the frame being doubled, as the 












MANUFACTURE OF SOAP, PART 2 


37 


original bottom carries the soap through the slabber and to 
the cutting table, by which time the original sides may be 
used to enclose a new frame of soap. 


59. Previous to crutching, or as it proceeds, a sufficient 
number of frames are put in readiness. When the crutchers 
are operated in pairs, an empty frame should stand ready to 
receive its charge as the preceding one is being filled. The 
filled frame, with the soap smoothed down into the edges of 
the frame by means of a short paddle and heaped up longitudi¬ 
nally in the middle, is pushed into its stand in the frame 
room. Here it is allowed to remain for a varying 
period, usually from 3 to 5 days, which period is 
determined by the demands of the factory, the sea¬ 
son, the character of the soap, and the temperature at 
which it was framed. 



GO. Before the steam-driven crutcher came into 
use, the soap was laboriously crutched in the frame 
with a hand crutch. The hand crutch, shown in 
Fig. 15, is still in use to prevent the filling material 
from settling to the bottom of the frame in soap that 
was crutched at too high a temperature; 
distribute the material used to produce a mottle ; or 
to distribute the reduction of temperature uni¬ 
formly throughout the entire mass as cooling Fig - 15 
proceeds, thus preventing the separation of the softer from the 
harder soap. 

With soap made from tallow, cottonseed oil, or grease, and 
rosin, and filled as has been noted, the sides may be removed 
from the frame on the second day after crutching. After 
removing the frame sides, the sides of the soap are scraped 
so as to remove any stains and blotches of adhering matter 
that may be present, and the soap is then ready to be slabbed. 


61. Slabbing Machine, or Slabber.—The device known 
as the slabbing machine , or slabber , varies greatly in simplicity 
and cheapness of mechanical construction. It is a development 
of the old hand method of drawing a wire in parallel lines 
longitudinally through the mass of soap. In the machine 







38 MANUFACTURE OF SOAP, PART 2 


slabber, whether hand- or power-driven, the direction of 
application of the power is reversed, the frame of soap being 
forced through a series of parallel wires arranged on a frame¬ 
work to the height of the soap to be slabbed. The essential 
mechanical features of the machine slabber are shown in 
Fig. 16. 

The power-driven slabber is automatic in action. The frame 
is run into the cage and the cutting head locked into place. 
The cutting head travels through the soap and returns, pushing 



the slabbed frame out of the cage when the slabber stops 
automatically. 


62. Piano wire is the best for soap cutting. This wire 
is mounted on the frame head a, Fig. 16, in parallel rows at a 
distance apart corresponding to the width or height of the im¬ 
pressed bars of soap. The frame of uncut soap is shown at b. 
By means of a key set in the sides of the frame head, the 
wires may be tightened or loosened as required. With soap 
that has stood for some time, it is often necessary to remove, 
for a short distance on both ends of the frame, the layer of 
soap that has become hardened. This permits the wires to 
enter the soap easily and to separate from it without the 





























































































































































MANUFACTURE OF SOAP, PART 2 


39 


abruptness that so often injures the wire; it also obviates 
undue stretching and breakage of the wires. 

63. Cutting the Soap.—From the slabber the soap is 
moved to the cutting table, where it is cut into bars. The 
fundamental principle of all cutting tables is shown in Fig. 17. 
A slab is lifted from the pile a lying on the frame bottom 
and is transferred to the table b ; it is then pushed lengthwise- 
through one or two wires held in the cutting head c. In this 
way, the slab is cut in*o two or three narrower slabs as wide 



Fig. 17 

I 

as the single bar of soap is long. These slabs are then cut 
at right angles by another attendant to dimensions corre¬ 
sponding to the width and thickness of a single bar. The 
last cutting movement pushes the slabs through the wires in 
the cutting head d, when, as single bars, they are pushed on 
a rack supported by an extension of the cutting table. Here, 
by a slight upward and horizontal motion, the individual 
bars are separated so that air may circulate between them. 
The separate racks are placed on a truck until its full quota 

















































40 


MANUFACTURE OF SOAP, PART 2 


has been received. The truck load is then taken into the 
drying room. 

64. The slabbing and cutting of soap are purely mechan¬ 
ical processes and have for their object the division of the 
frame of soap into bars. The greatest care to be exercised 
at these stages is to slab and cut the soap to such dimen¬ 
sions that the amount of waste is reduced to a minimum. 

Freshly cut soap is soft, sticky, and opaque, and, if properly 
crutched, should be homogeneous. It contains from 30 to 35 
per cent, of water, according to the manner in which the soap 
was settled and the nature of the additions during crutching. 
In calculation, it is considered that 100 parts of glyceride 
soap stock will yield 150 parts of finished soap. The yield 
is less with rosin alone, and with some stock it may be as 
great as 157 per cent. 

An analysis of pure settled soap at this stage presents the 
following data: 

Per Cent 


Fatty anhydrides.61.80 

Combined alkali. 7.21 

Anhydrous soap.69.01 

Water.30.99 

Total .100.00 


65. Drying the Soap.—Aside from the processes in the 
kettle, there is no stage in the manufacture of settled soap 
that requires greater care in its operation than the treatment 
received in the drying room. While improperly dried soap 
may cause no great trouble in the press, it is subject to rapid 
deterioration in appearance, and the influence of this one 
factor on its ultimate distribution demands that its final treat¬ 
ment in the factory be given the closest attention of the soap 
manufacturer. 

Previous to the introduction of the rapid-drying apparatus, 
the moisture in the exterior parts of the bar was allowed to 
evaporate spontaneously. By this method, the drying of soap 
was an extremely slow and unsatisfactory process, depending 









MANUFACTURE OF SOAP, PART 2 


41 


largely on atmospheric conditions. A stove in a closed room 
was a great improvement. This primitive method, with its 
manifest disadvantages, was succeeded by a system of hot-air 
circulation by natural draft. Steam heat by simple radiation 
from pipes was also employed, and with the introduction of 
forced draft, the elements of the system of drying in use 
at present were established. 

With laundry soap of good body, sufficient drying before 
pressing may be obtained in cool weather by standing the rack 
bottoms full of cut soap in front of an open window. It is 
necessary with this grade of soap only to get the surface 
skinned over enough so that the subsequent handling does not 
mar it and also prevents the soap from sticking to the 
dies of the press. However, in damp weather, and in summer, 
some artificial drying must be done. 

66. Purpose of Drying Room.—The purpose of the drying 
room is to hasten the evaporation of water from the surface 
of the bar, so that there may be formed a thin crust of 
comparatively hard soap. This crust serves to retard further 
evaporation from the interior of the bar and allows the bar 
to be pressed and stamped without the soap adhering to the 
dies. Without the formation of this skin of firm soap, press¬ 
ing and stamping cannot be done properly. 

On cutting a bar of soap into halves, this superficial drying 
becomes plainly evident. The soap when removed from the 
drying room and after being pressed has a smooth, glossy, 
and translucent surface, which condition is in a marked con¬ 
trast to that observed at the cutting table. 

67. During the drying process, from 3 to 5 per cent, 
of water has been expelled entirely from the surface of the 
bar, while the interior contains the amount of water originally 
present, namely, from 30 to 35 per cent. The inequality of 
moisture contents between the exterior and interior parts of 
the bar partly explains the sweating to which settled soaps are 
universally susceptible. 

This accumulation of moisture does not develop until after 
the bar is wrapped and packed. If a freshly pressed bar of 


42 


MANUFACTURE OF SOAP, PART 2 


soap without wrapping were allowed to remain exposed to 
the atmosphere, it would dry, but would not sweat, assuming, 
of course, that the atmosphere has not attained the dew 
point. The moisture in the interior of the bar has passed 
through the hard surface into the atmosphere, and this process 
will continue until an equilibrium of moisture contents through¬ 
out the bar has been attained. 

68. With soap wrapped and packed in a box, the con¬ 
ditions are entirely different. The tendency of the moisture 
to pass from the interior of the bar to the drier surface 
remains, but further evaporation from the exterior of the 
bar is checked. Here the moisture accumulates and softens 
the soap, which in turn adheres to the wrapper. This diffi¬ 
culty is overcome by using a parchment sheet between the 
soap and the outside wrapper. If the soap contains an exces¬ 
sive quantity of mineral salts, these are carried in an aqueous 
solution to the surface and on subsequent evaporation of the 
water form an incrustation. Boxed soap in storage should not 
be subjected to unnatural fluctuations of temperature. 

69. Drying Soap by Forced Ventilation.—The mechanics 
of the modern soap-drying room represent more the adoption 
of a similar process employed in other departments of industry 
than they do a natural evolution from previous efforts in this 
particular field. The use of centrifugal fans in the production 
of artificial draft dates from the 16th century, but it was 
not until Stevens’ experiments in the early part of the 19th 
century that the devices for artificial draft resolved themselves 
into the systems of ventilation known today, namely, the 
plenum and the vacuum, or, respectively, the forced and the 
induced, draft. 

In connection with the drying of soap, ventilating fans 
may be divided into two general classes: the centrifugal fan, 
or blower, and the propeller, or disk fan. The former is more 
generally confined to ventilation by forced draft and is designed 
primarily for removing air under pressure. Fans of the disk 
type, shown in Figs. 18 and 19, are not adapted to plenum 
ventilation, where it is desired to move large volumes of air 


MANUFACTURE OF SOAP, PART 2 


43 


quickly and under considerable resistance. They find extensive 
use and are very satisfactory for moving air under slight 
resistance, as under conditions met with in the ventilation of 
soap-drying rooms. 

70. Both systems of ventilation, the plenum and the 
vacuum, are used in the drying of soap. The equipment of 
a drying room under the plenum system comprises, as a rule, 



a disk fan, two arrangements of which are shown in Figs. 18 
and 19. In the arrangement shown in Fig. 19, the fan is 
operated either by a belt from shafting or by a direct- or belt- 
connected engine or motor and a sectional heater that consists 
of steam pipes enclosed in a sheet-iron case a, communicating 
with the discharge of the fan case b. Air may be forced 
through the heater and discharged at the desired temperature 
































































































































































44 


MANUFACTURE OF SOAP, PART 2 


into the drying room, or the fan may be interposed and air 
drawn through the heater and then discharged into the drying 
room. As the results produced are the same in either case, 
convenience of application will determine the arrangement. 

71. With forced draft, the drying room is best con¬ 
structed so that heated air enters at one end and leaves at the 
other, while freshly cut soap is introduced at one side, and, as 
the drying progresses, is withdrawn at the opposite side. The 
heater and fan may be placed at opposite ends of the room and 
the fan used to exhaust the warm and moisture-laden air. This 



Fig. 19 


arrangement presents an example of the vacuum system, or 
drying by induced draft. The combination of heater and fan 
shown in Fig. 19 is replaced with advantage by locating the 
heating coils at one end of the drying room or arranging them 
in rows throughout the drying room between the trucks of soap. 
The cheaper and simpler disk fan set in the framework of the 
wall, as shown in Fig. 18, is, with this arrangement for the 
drying of soap, equally efficient and satisfactory. The hot-blast 
drying apparatus shown in Fig. 19, although compact, may 
occupy valuable space. The exhaust-steam connections with 
the necessary insulation are simple and easily made. 





















MANUFACTURE OF SOAP, PART 2 


45 


72. Heating of the Drying Room.—By distributing the 
pipes of the sectional heater throughout the drying room in 
rows parallel with the trucks of soap and under openings 
immediately above for the admission of cold air, not only is 
a greater uniformity of the drying process obtained, but the 
use of the cheaper disk fan, which is admirably adapted for 
ventilation by exhaustion, is permitted. Exhaust-steam con¬ 
nections are made through the floor, and by means of suit¬ 
ably placed valves, exhaust steam may be cut off from any 
section, thus varying the capacity of the drying room at will. 

73. In the drying process, air fulfils two functions: it 
carries to the moist soap heat necessary for the evaporation of 
the water and it serves as a vehicle for the removal of the 
vapor. The capacity of air for heat is very small, its specific 
heat being only .238, with water as 1; its capacity for vapor 
depends directly on its temperature and its relation to the 
dew point, naturally diminishing as the point of saturation is 
reached. With a rise of temperature, the capacity of air for 
moisture increases. It is estimated that air at 72° F. has a 
threefold greater capacity for aqueous vapor than the same 
volume at 42° F.; at 172° F., its capacity for vapor is more 
than eighty times as great. Increase of temperature thus 
means the more rapid formation of vapor, with a much greater 
increase in the capacity of air for absorbing it. 

74. Requirements of the Drying Room.—The essential 
requirements of the heating and ventilating apparatus of the 
drying room are that a large volume of air be provided at the 
required temperature and that this be maintained in rapid 
circulation. A comparatively low temperature, namely, 90° to 
100° F., is productive of the best results. Air maintained 
at a temperature in excess of 100° F. for a long period causes 
the soap to undergo an appreciable softening, with more or 
less discoloration. 

The temperature at which soap will melt depends primarily 
on the nature of the stock and the proportion of water present. 
In the drying of green soap, it is desirable that the currents of 
warm air circulate lengthwise of the bar, in order that the 


394—8 


46 


MANUFACTURE OF SOAP, PART 2 


largest extent of evaporative surface may be exposed and the 
drying process thus hastened. The duration of the drying 
period is easily learned by experience, from the appearance of 
the bar; it varies from 6 to 12 hours. 


75. Pressing of Soap.—Hard soap was originally sold in 
the United States in bulk. Later, the soap was cut into bars 

and packed, with the 
wrappers in bulk, in a 
box, the retailer him¬ 
self wrapping the soap 
as sold. Under pres¬ 
ent conditions, how¬ 
ever, the freshly cut 
bar is pressed, stamped, 
and wrapped. 

In Fig. 20 are shown 
the essential features 
of a foot-power soap 
press. This machine is 
arranged so that the 
operator can deliver a 
sudden blow to the 
cake of soap placed in 
the die box a. The 
thumb and forefinger 
of the right hand are 
used to place the soap 
in this die box. An 
operator on a press of 
this kind will press, 
thirty bars per minute. 
To prevent soap from 
adhering to the die b, the cake is placed lightly on a bunch of 
waste saturated with brine or a mixture of vinegar and water 
that is usually located at the right of the die box a. After the 
blow has been delivered by the right foot placed on the lever c, 
the upper die b is lifted by the counterpoise d, which also serves 



Fig. 20 
























































MANUFACTURE OF SOAP, PART 2 


47 


to add momentum to the force of the blow, and a lever action 
lifts the pressed bar out of the die box a. The bar is then 
transferred, by the left hand of the' operator, to a table at his 
left. The foot-power soap press is built in a number of styles, 
some being partly operated by steam, as shown in Fig. 21. 

76. Steam Foot-Press.—The steam foot-press. Fig. 21, 
is provided with a steam cylinder a, the piston b of which is 



directly connected with a lever c that controls the dies d and e. 
A system of valves is arranged at f and g, from which points, 
by a slight pressure of the foot on the treadle h, steam is 
admitted to the cylinder a and a quick, powerful blow is given 
to the soap placed over the die box, the lower die e of which 
is elevated as shown. The lever returns instantly, withdrawing 
the upper die and elevating the lower one, from which the cake 



































































48 


MANUFACTURE OF SOAP, PART 2 


of soap is removed by the left hand of the operator. With 
rapid work, upwards of 1,500 cakes an hour can be pressed 
on a machine of this type. This kind of press is not used 



extensively at the present time; it is replaced by more modern 
machines, which are entirely automatic and give a much higher 
output. 






































MANUFACTURE OF SOAP, PART 2 


49 


77. Automatic Steam-Power Soap Press.—The belt- 
driven, automatic soap press is a direct development of the 
old foot-power press, and arose from a demand for greater 
rapidity of operation. Several styles are on the market, with 
a guaranteed capacity of from 60,000 to 75,000 cakes per day 
of 10 hours. They are perfectly automatic in their action, 
require but little attention, and for a factory producing upwards 
of 400 boxes of soap per day, such a machine is a safe purchase. 

The more improved forms admit of interchangeability of 
the dies, thus permitting the soap manufacturer to use any 
die that he may have in stock. Thus all the brands of a 
single factory can be pressed on the same machine, with no 
longer time required to change the dies than on the old-style 
foot-press. On the. high-speed presses, a dilute solution of 
acetic acid (3 to 4 per cent.) is allowed to drip on the dies to 
prevent sticking. 

78. In Fig. 22 is shown one of the latest forms of steam- 
power soap press. To describe it briefly, power is applied 
to the pulley a, which in turn operates the feeding belt running 
on the surface of table b. This belt carries the cake of soap 
to the drop box c, down which it falls between the two dies 
impelled in a horizontal plane at d. The cake of soap as 
it falls down the drop box c is caught between the two dies, 
pressed, and dropped on the belt e, which carries the pressed 
bar to the wrapping bench f, where it is wrapped and then 
packed in boxes. 

79. In Fig. 23 is shown a three-die rotary soap press. 
This machine consists of double cylinders a and b placed 
end to end, in which rotate cams that automatically bring 
together and withdraw horizontally two dies that meet in 
their corresponding die box, of which three are arranged 120° 
apart. The dried soap from the racks is placed on the feed¬ 
ing belt e, from which each bar is singly moved forwards 
to the die by a finger on the chain belt passing over the pulley d, 
to which power is applied at c. A set of dies is shown at f. 
The pressed soap is dropped on the belt running in the box g 
and is conveyed to the wrapping bench. 


50 


MANUFACTURE OF SOAP, PARI' 2 


80. Wrapping by hand is done in small establishments. 
It has been superseded in the larger ones by automatic power 
machines, the soap coming from the presses feeding directly to 



Fig. 23 

belts that supply the wrapping machines. The press just 
described requires two wrapping machines. The wrapped soap 

is packed into the box as it 
leaves the machine. 

Among the many advan¬ 
tages possessed by auto¬ 
matic soap presses are 
chiefly the perfect work, 
capable, at a maximum 
speed, of 150 bars per 
minute; the regulation of 
the pressure to suit the character of the soap; and the insur¬ 
ance of safety to the operator from loss of fingers. The auto¬ 
matic power press of the capacity stated will do the work of 
five foot-presses with one-third the labor. 


























































MANUFACTURE OF SOAP, PART 2 


51 


81. Soap Dies.—The kind of die to be used is determined 
by the kind of soap to be pressed. The function of a die is 
twofold: it forms the yielding mass of soap into a definite 
shape and imprints on the cake thus formed, in either elevated 
or sunken letters, or both, usually the brand of the soap and the 
name of the manufacturer or vender. 

The earliest form is the hand stamp, shown in Fig. 24, by 
means of which the brand or maker’s name is impressed on 
the freshly cut bar. 

82. The second form is the box die shown in Fig. 25. In 
this form of die, the mold feature is introduced in pressing 
the soap from above and below in 
an enclosed space called a box. 

The upper die a and the lower die b 
fit closely to the interior of the box 
c. They are so adjusted with the 
press as to cause their respective 
downward and upward movement 
at a separating distance correspond¬ 
ing to the thickness of the pressed 
bar, which dimension the thickness 
of the unpressed bar closely approximates. There is thus 
insured such a distribution of the soap in the mold as to fill 
every part of it. 

The same box and dies may be used for different brands, 
by means of detachable name plates. In fitting the box to 
the bedplate of the soap press shown at e, Fig. 20, by means 
of the shanks shown at d, Fig. 25, care should be taken to 
insure a perfectly vertical motion of the upper and lower 
dies; otherwise, they will rub against the interior sides of the 
box, with the result that the accuracy of the die will soon be 
destroyed. 

83. In the molding and stamping of milled soap, dies of 
a different construction must be used because of the greater 
firmness of soap of this character. A powerful and sudden 
blow must be delivered, and the construction of the die must 
be such as to expel all surplus soap from the cavity, instead 



























52 


MANUFACTURE OF SOAP, PART 2 


of, as in the more yielding laundry soap, forcing this surplus 
into every part of it. 

The pin, or shoulder, die is so called from the use of pins 
and sockets to guide the upper and lower dies, thus preserving 



their accuracy. The term shoulder has reference to the base 
supporting and receiving the four pegs. As shown in Fig. 26, 
this third form consists of two dies, (a) being the top die 
and ( b ) the bottom die, without a box, each forming the face 
and one-half of the cake. The edges c and c' of the dies 
strike together, thus forcing out all surplus soap. The guide 
pins d, d' d", and d'" of the top die serve to guide it squarely 



Fig. 27 

on the bottom die. The shoulders of the bottom die, receiving 
the guide pins in the corresponding holes d, d', d", and d'", 
bear the force of the blow, and preserve the cutting edges 
c and c\ These dies are also made with removable panels. 














































































































































53 



Fig. 23 




































































































































































































































































































54 


MANUFACTURE OF SOAP, PART 2 


or name plates, thus permitting a number of brands to be 
stamped with the same die by inserting a different name plate 
in the base of the bottom die. 

84. The fourth form is a combination of the pin, or 
shoulder, and box dies, and in addition to possessing the 
qualities of each, it admits of the pressing of cakes of different 
thicknesses and weights by virtue of the removable lower 
die placed in the box. As shown in Fig. 27, a is the remov¬ 
able lower die, which is made in varying heights so as to 
produce a bar of corresponding thickness. It fits into the 
box b, which is fastened by the shanks c to the bedplate of 
the presses shown in Figs. 20 and 21. The guide pins of the 
top die e are shown at d, and shoulders of the lower die at /. 

The dies are made of gun-metal alloy or rolled brass. 
They should be substantially made with all moving parts 
carefully fitted. The engraving should be so executed, with 
letters or figures of uniform bevel, as to produce in the soap 
clear-cut and even characters, more especially when these are 
in relief. The workmanship of the die is shown at once in 
the appearance of the pressed soap. A good die greatly 
improves the appearance of an inferior product. Toilet soap 
is stamped on foot-presses, the automatic press having not 
as yet proved satisfactory for stamping milled soap. 

85. Plans of Two Types of Soap Factory. —Two general 

types of soap factory are shown in Figs. 28 and 29, Fig. 28 
showing all the equipment on one floor, and Fig. 29 the 
gravity plan as used by the larger plants, by which the soap 
is boiled on the top floor and finished on the way down. 
From these two plans, in conjunction with the methods and 
apparatus described in the preceding articles, each operation 
may be traced. 




























































































































































































































































































































































MANUFACTURE OF SOAP, PART 2 


55 


SEMIBOILED SOAPS 

86. The term semiboilcd, as applied to soap, refers to 
a soap that has not been grained, the saponification being 
completed in one change and the soap strengthened and 
settled in the following one. As the soap is not grained, in 
which process glycerine is separated, the kettle will contain, 
on the completion of the process, all the material that has 
been added to it. In semiboiled soap, rosin may be used as 
an ingredient, but the process is generally used only for 
straight glyceride stock. 

87. As no impurities are removed in the waste lye formed 
by graining, it is necessary, in order to produce a superior 
quality of goods, that the stock used be of good grade.' This 
process is often resorted to for the manufacture of the base 
for cheap toilet soaps. It is used generally for preparing 
the soap base for soap or washing powders, and is more 
quickly carried out than is the manufacture of settled soap. 
The stock can be killed (saponified) in the early forenoon, 
strengthened in the afternoon, and pumped to the crutcher, if 
a filled soap or a soap powder is to be made, or directly into 
the frame, if intended for toilet soap, on the following morn¬ 
ing. If it is desired to save the glycerine and to remove the 
impurities as well, the soap may be grained sharply after 
the stock has been killed, the waste lye withdrawn on the 
following morning, and the soap carefully strengthened, 
settled, and pumped from the kettle on the third day. 

88. The semiboiled process is primarily a cheap method 
of soap manufacture, with economy in fuel, labor, and time. 
The best plan, however, is to give the soap a simple puri¬ 
fication by graining it sharply, thus prolonging the time 
consumed in manufacture by one day. If this is done, the 
grained soap should stand overnight before drawing the lye. 
By doing so, the volume and depth of color of the niger is 
greatly reduced. 

The semiboiled process is used as well for the manufacture 
of soft soaps, of which textile soap is a variety, and for green 


56 


MANUFACTURE OF SOAP, PART 2 


Castile soap made from olive-oil foots. A desired characteristic 
of the latter soap is the green color arising from the green 
coloring matter, or chlorophyl, present in the rind and pulp 
of the fresh olive. This soap is never grained. In graining, 
the coloring matter would be discharged into the waste lye, 
with the result that the finished soap would bleach rapidly 
and unequally on exposure, thus detracting from its appearance. 

89. Manufacture of Soft Soap. —As the semiboiled 

process is used for the manufacture of soft soap, the boiling 
of this quality of soap will be discussed in outlining the 
practical features of the process. 

Straight tallow or good grease stock, to which may be 
added some cottonseed oil, is run into the kettle on open steam. 
According to Table XIII, Manufacture of Soap, Part 1, for 
saponifying 10,000 pounds of tallow with caustic-soda lye of a 
density of 20° Baume, made from 74 per cent, caustic, 9,795 
pounds will be required. As tallow is a stock that is easily 
killed and gives well-defined indications of conditions in the ket¬ 
tle, practically all this lye may be added by the time the stock is 
in. Saponification, however, progresses in the meantime. 
The chief care is to avoid bunching, by boiling the contents 
of the kettle vigorously. Open steam is used throughout the 
process. 

90. In the manufacture of settled rosin soap, a hard soap 
was produced; in the present case, however, it is desired to 
turn out a soft soap made with a soda base. According to 
an old definition, a soft soap is one in which the alkali used 
is potash. That definition is obsolete, for the hardness of 
a soap does not depend primarily on the nature of the alkali 
present, but on the degree of hydration of the soap. A hard 
soap can be made of potash and olein, which were the ingre¬ 
dients of the original Castile soap. 

With settled hard soap, a yield of 150 per cent, is generally 
obtained; with soft soap, a yield may be obtained varying 
from 225 to 240 per cent. In fact, the yield may be any 
amount up to 400 per cent., according to the purpose for which 
the soap is intended. 


MANUFACTURE OF SOAP, PART 2 57 

91. After the stock has been thoroughly killed, the soap 
is opened slightly with caustic and boiled. This treatment is 
equivalent to a strengthening change without the intermediate 
graining. After having boiled quietly on this strength for some 
time, with an occasional addition of caustic lye as it has been 
absorbed, add water gradually until the soap closes. There 
is now in the kettle the soap-maker’s 150 per cent, yield, and 
the soap is in a condition similar to that of settled soap on 
the settling change. The degree of hydration is determined 
either by the specifications of the purchaser or by the price 
obtained for the product. After the soap has been closed, 
water is added slowly, care being taken to boil it through 
the mass thoroughly after each addition, until the soap has 
been brought to that consistency determined by experience. 

92. A more satisfactory method, and one depending less 
on the variable and confusing conditions in the soap kettle, is 
to add the regulated amount of water to the soap in the 
crutcher. After thoroughly incorporating the addition in the 
crutcher, the soap is dropped into tight, weighed barrels and 
allowed to cool. The barrels are then headed and weighed. 
There is no market in the United States for package-made 
soft soap; it is sold in bulk to institutions for cleansing pur¬ 
poses, and in greater quantities to textile manufacturers. 

93. When the soap is hydrated in the kettle, the yield is 
variable, owing to the difficulty of determining the loss of 
water by evaporation, and in successive boils it may vary 
several per cent. In the manufacture of soft soap with 
unmixed stock, as tallow alone, there is not sufficient dif¬ 
ference in the amounts of the various glycerides present to 
produce the figging so often desired in a soap of this character. 
With soft soap made from cottonseed oil, with a small pro¬ 
portion of tallow, the figged appearance on cooling may easily 
be obtained by virtue of the different solidifying points of 
soaps made from glycerides of different melting points. 

94. Soft soap made from caustic potash will admit of a 
higher yield within the limits of the quality of the product 


58 


MANUFACTURE OF SOAP, PART 2 


desired. This arises from the greater combining weight of 
caustic potash, the molecular weight of caustic potash being 
56, while that of caustic soda is 40; also from the fact that a 
potash soap in a hydrated condition will stand a greater 
amount of saline filling than will a soda soft soap. 

Rosin is used to a great extent in soft soaps, but it should 
never be present in textile soaps. Linseed oil is extensively 
used in European practice, and, in fact, may be said to be 
the chief ingredient. Soft soaps admit of adulteration to a 
high degree, the principal cheapeners and adulterants being 
aqueous solutions of sodium silicate, soda ash, and potassium 
chloride; starch is also largely used. 

95. Calculation of Yield.—To ascertain the net per¬ 
centage of yield, simply divide the net weight of soap made 
by the weight of soap stock used. To arrive at the total 
yield, the numerator is increased by the weight of the filling 
material added to the soap in the crutcher or in the kettle. 


COLD-PROCESS SOAP 

96. In the discussion of the settled and semiboiled proc¬ 
esses of soap manufacture, it was learned that the latter is 
the more economical, and for the manufacture of soaps of a 
certain character, it is the preferable one. The ease with 
which the soap can be purified by graining and removing the 
waste lye containing the impurities, indicates the looseness 
of the line of demarcation between the two processes. In the 
discussion of the manufacture of soap by the cold process, a 
method that surpasses all others in the economy of every 
element entering into the cost of production, is introduced. 
The method, however, possesses certain paramount dis¬ 
advantages, which restrict its use to a very limited field, 
notwithstanding the large amount of soap of this character 
that is produced. The mechanical equipment required con¬ 
sists simply of tanks containing the. fat, oil, and caustic-soda 
lye; a crutcher in which the ingredients are mixed; and 
frames to receive the mixture and in which, under favorable 



MANUFACTURE OF SOAP, PART 2 


59 


conditions, the chemical reaction of saponification continues 
to completion. 

With such simple and comparatively inexpensive factory 
equipment, it will be evident that the proportion of fixed 
charges in the cost of the product is very small. Experience 
is the chief and most important asset, without which, not¬ 
withstanding the simplicity of the process, satisfactory results 
cannot be assured. 

97. The term cold process is loosely descriptive. The 
saponification is not conducted in the cold, for the heat gen¬ 
erated by chemical combination is considerable. The term 
has reference chiefly to the fact that heat is not employed as 
in the two general processes previously described, only enough 
heat being used to insure the liquid condition of all the 
ingredients. 

The theory of the process is very simple. The essential 
requirements are that the ingredients taking part in the reaction 
be intimately mixed. To effect this, the fat or oil must 
be in a liquid state and the caustic-alkali solutions must be 
maintained at such a temperature that when the stock and 
alkali are mixed, neither will cool the other to stiffness 
before every particle of the glyceride is brought into contact 
with the alkali. Even in the daily working of the process, 
it is a very difficult matter to maintain uniform conditions 
and to insure the complete absorption of the alkali. As the 
process is ordinarily practical, saponification is invariably 
incomplete, with more or less free fat and free alkali remaining 
in the finished product. This is the chief disadvantage of 
the process, and is the one that greatly restricts the use of 
cold-process soap for toilet purposes. 

98. To secure satisfactory results in the practical work¬ 
ing of the process, it is necessary that the caustic alkali be 
of high grade, not of lower quality than 76 per cent., and 
that the glyceride stock be fresh and pure. Without these 
primary qualifications, good results under no circumstances 
can be assured; but with them, the prime essentials of 
satisfactory work are obtained. 


60 


MANUFACTURE OF SOAP, PART 2 


Coconut oil, either alone or in admixture with tallow and 
cottonseed oil, is chiefly used for cold-process soap. The 
rapid absorption of alkali at a comparatively low temperature, 
with the production of a smooth, clear soap that will neither 
crack nor warp on aging and that will admit the incorporation 
of a large amount of filling, make this oil especially adapted 
as a raw material for soap of this character. With inferior 
grades of coconut oil, boiling on strong caustic of 36° Baume 
with open steam will remove what free fatty acids there are 
present, and these, with the impurities, will easily settle out. 
The same preliminary purification is also required for tallow. 

The manufacture of cold-process soap received great 
impetus from the manufacture of high-grade caustic soda; the 
impurities always present in low-grade caustic interfered 
greatly with the satisfactory working of the process. 

99. Manufacture of Cold-Process Soap. —To explain the 
process in practical detail, the manufacture of cold-process 
soap from 500 pounds of coconut oil will be discussed. By 
referring to Table XII, Manufacture of Soap, Part 1, it will 
be found that coconut oil will absorb about 17.6 per cent, of 
chemically pure caustic soda. This amount is equivalent to 
18 per cent, of 76 per cent, commercial caustic; therefore, 90 
pounds of caustic soda of this grade will be required for 
saponification. 

A caustic-soda lye of 35° Baume, made from 76 per cent, 
caustic, contains 28.28 per cent, of sodium hydroxide. There¬ 
fore, to furnish 90 pounds of sodium hydroxide, 318 pounds of 
35° Baume caustic lye, made from 76 per cent, caustic, will 
be required 

100. The purified coconut oil at a temperature of 115° to 
120° F. is run into the crutcher, and the latter is then agitated. 
The required amount of lye is then run in, and crutching 
is continued until a portion of the mass removed on a paddle 
appears clear and homogeneous. This condition can be 
ascertained only by experience, and under no consideration 
should the contents be removed from the crutcher until the 
most thorough mixing possible has been effected. The mixing 


MANUFACTURE OF SOAP, PART 2 


61 


period need not exceed from 20 to 30 minutes, and with 
experience the time required is usually less. The mass is 
then dropped into frames, which are removed and carefully 
covered with soda-ash bags or other suitable material so as 
to prevent too rapid cooling. The frames should not be 
exposed to currents of cold air nor in any way subjected to 
rapid cooling. 

101. There were added in the crutcher 500 pounds of 
coconut oil and 90 pounds of solid caustic dissolved in 228 
pounds of water. This mixture yields a soap that, in so far 
as hydration is concerned, corresponds to the composition 
of unfilled settled soap. A yield of practically 63 per cent, 
has been obtained. By adding tallow and cottonseed oil in 
suitable proportions, the cost of the soap may be greatly 
reduced; also, the yield may be increased and the cost greatly 
reduced by the addition of sodium silicate, soda ash, pearl 
ash, mineral soap stock, starch, or talc. 

102. All the filling material in cold-process soaps is 
generally mixed with the lye previous to being added in the 
crutcher. If it is desired to perfume the soap, the essential 
oil is added directly to the mass in the crutcher toward the 
end of the mixing process. 

It should be borne in mind that the more highly filled a 
cold-process soap is, the more is the process of saponification 
retarded through the presence of inert material. Cold-process 
soap will admit of more filling than will settled soap without 
a corresponding deterioration of appearance on aging. 

The substitution of caustic potash for a portion of the 
caustic soda is desirable, as a clearer, smoother, and milder 
soap will result. 

103. In the procedure just described, there has been no 
interference on the part of the attendant. The ingredients 
were mixed in the calculated proportions, and the mixture 
thus obtained was treated mechanically in the hope that the 
results would be satisfactory. As experience in the operation 
of the process is acquired, the treatment may be modified 

394—9 


62 


MANUFACTURE OF SOAP, PART 2 


according to the judgment of the attendant. In the following 
procedure the judgment of the manufacturer is called into play. 

Add the coconut oil at a temperature of 115° F. to the 
crutcher and start it slowly; then add gradually the caustic- 
soda lye, which was prepared at the same temperature. 
When all the caustic-soda lye has been added, continue 
crutching at the same or only slightly greater speed for a 
period of 5 minutes. At the expiration of this period, stop 
the crutcher and enclose it with a cover and soda-ash bags 
so as to retain the heat. Allow the mass to stand for an 
hour and then start the crutcher slowly. If a simple mixer 


TABLE VI 

FORMULAS USED IN MAKING COLD-PROCESS SOAP 


Ingredients 

Formula No. 1 
Pounds 

Formula No. 2 
Pounds 

Tallow. 

75 

75 

Coconut oil (Ceylon) .... 
Caustic-soda lye (35|° Baume) 

25 

25 

made from 75 per cent, 
caustic. 

75 

70 

Silicate of soda, N grade . . 

125 

100 

Pearlash lye, 36° Baume . . 

20 

17 

Amount of soap produced . . 

320 

287 


of style A, Fig. 6, is used, the contents should not rise 
above the level of the topmost horizontal arm; if it does, this 
portion of the contents will not be thoroughly mixed. With 
a crutcher of style B, Fig. 7, the contents should not rise 
above the level of the central cylinder enclosing the screw. 
With a steam-jacketed crutcher, the process can be more 
easily controlled through the use of steam, should the tem¬ 
perature fall below that ascertained by experience to be best, 
namely, 160° F. If at this stage the soap should show an 
excessive sharpness to the tongue, a few pounds of coconut 
oil may be added and crutched in until the soap tastes free 















MANUFACTURE OF SOAP, PART 2 


63 


from caustic. On the contrary, should the soap, after the 
maximum heat of the reaction has been evolved, be neutral 
to the taste, a few pounds of 15° Baume caustic-soda lye 
may be added and thoroughly incorporated. After these 
adverse symptoms have been corrected, start the crutcher at 
full speed and continue crutching for fully 20 minutes, until 
the mass rises white and smooth to the top of the crutcher. 
The perfume is now crutched in and the soap framed. 

104. Manufacture of Cold-Process Soap Directly in the 
Soap Frame.—It is possible to make a fairly satisfactory 
cold-process soap directly in the soap frame, thereby elimi¬ 
nating the crutcher. Elkington has given instructions for the 
manufacture of cold-process soap by this method according 
to the formulas given in Table VI. 

105. Weigh out the proportions of tallow and coconut 
oil required for a frame of soap into a tight frame. Weigh 
out the quantity of caustic-soda lye required into a separate 
vessel; also weigh out the proportion of silicate of soda 
needed into another vessel. The pearlash (crude potassium 
carbonate) solution is then weighed out and mixed with the 
silicate of soda. When all is ready for mixing, the tempera¬ 
ture of the tallow and coconut oil in the frame should be 
from 145° to 150° F. in cold weather and from 125° to 130° F. 
in warm weather. The caustic-soda lye, and silicate of soda 
mixture should be at the normal temperature of the factory. 

When the temperature conditions are as just stated, the 
caustic-soda lye is run alone and quickly into the frame 
containing the mixed tallow and coconut oil, the mass in the 
meantime being crutched vigorously from the bottom of the 
frame. After adding the caustic-soda lye, crutching should 
be continued until the mass begins to thicken. The mixture 
of sodium silicate and pearlash lye is now added quickly, 
with continued crutching. 

106. After the last addition, the mass in the frame will 
be thinned out considerably and with continued crutching will 
gradually acquire a thick, creamy consistency. The two hand 


64 


MANUFACTURE OF SOAP, PART 2 


crutches are now removed, and the frame is carefully covered 
and allowed to stand without disturbance until the soap is 
cold. If the soap is to be perfumed, the essential oil is 
stirred in with the silicate of soda mixture and added with it. 
If the frame must be moved from where the soap is made, 
move it quickly before the silicate of soda mixture is added; 
then add this mixture at once and finish the soap as directed. 
The cold process is primarily a quick process, the tardy 
addition of any ingredient being sufficient to mar the results. 

107. For a 1,000-pound frame, the caustic-soda lye must 
be run into the soap stock in from 90 to 120 seconds. The 
addition of the silicate of soda mixture should also not require 
more time than this. Two crutches (see Fig. 15) should be 
used, the work carried on quickly, and the bottom of the frame 
reached at each stroke. With satisfactory conditions of tem¬ 
perature, the time required in preparing a frame of cold- 
process soap as just outlined should not exceed from 12 to 16 
minutes. Care should be taken not to crutch the mass too 
long. To insure a smooth soap, crutching should be stopped 
as soon as a mark made on the surface of the soap will remain, 
and under no circumstances should the frame be disturbed 
until the contents is cold. With good, firm tallow, cottonseed 
oil may be substituted for it to the extent of 30 to 50 per 
cent., and less if the tallow is softer. With soft stock, more 
time will be required for cooling. 

108. The apparatus used in cold-soap manufacture admits 
of very convenient arrangement. . The soap-stock and alkali 
tanks should be placed on an elevation above the crutcher 
and should be provided with closed steam coils for heating 
the contents to the required temperatures. 

Successful operation can only be carried out by weighing 
the stock and the alkali. If two scales are available, tanks 
sufficiently large to hold stock for five frames may be used, 
the weight each time being taken by difference. The stock 
and alkali are run from the storage tanks to the weighing 
tanks, and from there to the crutcher. If only one scale is 
available, the tank need be only large enough to charge one 


MANUFACTURE OF SOAP, PART 2 


65 


frame, the stock being weighed out and emptied into the 
crutcher, and after this the alkali and filler, if any is used. 
In this manner, mistakes in the weights of the material used 
may be avoided. 

109. In summing up the advantages and disadvantages 
of the cold process, it may be stated that the soap is simply, 
easily, and quickly made, with but little outlay for plant and 
labor. It admits of a greater yield than that furnished by 
any other process for the manufacture of hard soap. A well- 
made cold-process soap has not only a better appearance 
than a boiled soap, but retains its good appearance longer. 
It admits of a greater degree of filling than does a settled 
soap. The process differs greatly from the boiled processes 
in one important particular, namely, that small quantities can 
be made at a time. The process is used extensively for cheap 
toilet soaps, in few instances for laundry soap, and almost 
entirely in the manufacture of chipped soap that is sold to 
laundries. 

As ordinarily practiced, the process does not admit of 
complete saponification, as do the boiled processes, the soap 
invariably containing, according to the care and experience 
used in its manufacture, greater or smaller amounts of free 
caustic alkali and uncombined fat or oil. Rancidity soon 
develops from the presence of uncombined oil. This is the 
chief, and practically the only, disadvantage of the cold process. 







MANUFACTURE OF SOAP 

Serial 2055C (PART 3) Edition 1 


REMELTING OF SOAP 

1. Purpose of Remelting. —Soap scraps result from 
various sources, which may be enumerated in the order of their 
occurrence, namely, frames of soap that have cracked or 
fissured or for any cause are not suitable, either in whole or in 
part, for slabbing and cutting; scrapings from frame bottoms; 
defective bars and trimmings from the cutting table; spoiled 
bars from the soap press; and unsatisfactory boxed soap 
returned by the trade. Such soap contains its proportion of 
the filling added in the crutcher, and if the soap were returned 
directly to the soap kettle, this filling would be lost in the 
waste lye. The function of the remelter is to remelt these 
scraps, and when melted, the soap is crutched and framed as 
before. Whenever possible, it is more economical to use up 
the clean scrap in the crutchers. The small amount that 
cannot be utilized in this manner may be boiled over again. 

2. Some perfume and usually a small quantity of soda-ash 
solution are generally added to the remelted soap in the 
crutcher. The texture of remelted soap, when cut and 
pressed, differs from that of freshly pressed soap in being 
less clear. 

When possible, it is always best to place the remelter 
above the crutchers and not to crutch the remelted soap alone, 
but to mix it with fresh soap coming from the kettle. The 
amount of soap, or scrap, to be remelted is usually equal to 
about 10 per cent, of the output of the factory, so that if 


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2 


MANUFACTURE OF SOAP, PART 3 


frames having a capacity of 1,200 pounds are used, each 
crutcher should have 120 pounds of remelted soap added to 
it. By following this method, a uniform product is possible 
one feature of the soap trade that is very essential in order 
to insure a successful and profitable business. 

3. Remelters.—As shown in Fig. 1, a remelter con¬ 
sists of a sheet-steel tank with a system of closed steam 
pipes b arranged vertically inside and also a system of closed 



steam pipes c arranged horizontally on the bottom and a 
short distance above the outlet e , the pipes c being connected 
with pipes b. A coarse wire netting d serves as a strainer; 
it is placed below the steam coils c and above the open steam 
jet /. The pipe i carries steam to the upright system b; the 
exhaust pipe j carries the water of condensation from the 
horizontal system c; and the live-steam pipe k supplies 
the steam jet /. The remelter is usually covered with insulaU 






























































































































MANUFACTURE OF SOAP, PART 3 


3 


ing material, to retain the heat, and is surmounted by a 
wooden casing so as to receive the soap on the floor above. 
The steam pipes are so arranged as to distribute the heat 
uniformly throughout the mass and to interfere least with 
the flow of the melted soap, by gravity, from the bottom of 
the remelter. 

4. When sufficient scrap for several frames has accu¬ 
mulated in the remelter, steam is admitted into the closed 
coils and the adjacent soap is melted. Live steam is then 



introduced for a period of 10 minutes in addition to the 
closed steam. At the expiration of this period, the remelted 
soap should flow freely from the outlet. The live steam is 
now turned off. When a sufficient mass has melted to 
charge the crutcher, which is usually placed below the remelter 
in factories where a separate remelter is used, framing is 
begun and continued as fast as the soap melts. The remelted 
soap withdrawn is replaced by unmelted soap, which sinks by 
gravity from the wooden casing surmounting the remelting 
tank. 





















































4 


MANUFACTURE OF SOAP, PART 3 


5. Remelting Crutcher.— When the size of the factory 
does not warrant the installation of a separate remelter, 
the latter may be combined with the crutcher, as shown 
in Fig. 2. The remelting crutcher, as this device is called, 
is a crutcher in which the inner concentric cylinder is 
replaced by vertical, closed steam pipes surrounding the 
screw. Steam is admitted into the vertical, closed steam 
pipes a through the valve b. Live steam is introduced 
at c, and the water of condensation is withdrawn from 
the closed steam pipes at d. The outlet of the crutcher 
is at e. The remelting of soap in this device is carried on 
practically the same as with the regular remelter. Soap 
scrap may be introduced by gravity from a receptacle placed 
above the crutcher. 


MANUFACTURE OF TOILET SOAP 


MILLED-PROCESS SOAP 

6. The manufacture of toilet soap requires the installa¬ 
tion of expensive machinery and a greater degree of skill 
than is necessary in the manufacture of laundry soap. Not 
only the cost of plant and the superior skill required in man¬ 
ufacture, but the experience and ability required in market¬ 
ing the product, confine its manufacture to a comparatively 
limited number of plants. The manufacture of toilet soap 
in the United States dates from 1844, at which time a French¬ 
man, Jules Haul, made soap of this character with very 
primitive apparatus, in Philadelphia. Since the original 
manufacture of toilet soap in the United States, just noted, 
American skill and experience, together with the superior 
mechanical appliances employed, have so far advanced that 
the toilet soap produced in this country is equal to that pro¬ 
duced elsewhere in the world. 

7. Although toilet soap can be made by any of the three 
processes previously described, the term generally has ref¬ 
erence to what is called a milled soap , meaning by this a soap 




MANUFACTURE OF SOAP, PART 3 


5 


that, after having been partly dehydrated, is kneaded into 
films of dough-like consistency in a machine called a mill. 
The soap is then compressed into an elongated bar, which is 
cut into sections and pressed into separate cakes. 

By this process of manufacture it is possible to combine 
the finest style and finish with superior quality and durabil¬ 
ity. Owing to the partial dehydration to which the toilet- 
soap base has been subjected, its milling, and the subsequent 
compression in the plodder, soap manufactured in this man¬ 
ner is the most economical for toilet purposes. 

8. Toilet-Soap Base. —The manufacture of toilet soap 
requires first the manufacture of what is commonly called 
the toilet-soap base. This may be either a well-made settled 
soap, a semiboiled soap, or a cold-process soap. The principal 
requirements of a good toilet-soap base are that it be made 
from fresh material of good quality, be free from impurities, 
completely saponified, perfectly neutral, and of a good, tough 
grain. In large establishments, the manufacture of the toilet- 
soap base is usually entrusted to one man having special 
skill in the boiling of soap for this purpose. The nature of 
the stock used is very important. 

Good, fresh tallow, with the characteristic shortness 
of grain of the soap made from it, softened by the addition of 
suitable proportions of cottonseed oil or a good grade of 
white grease, and smoothed with a proportion of coconut oil, 
will make a first-class toilet-soap base. 

9. The formulas of the toilet-soap base vary greatly. 
Castor oil and lard may be used to make the soap milder 
and to admit of a finer finish in the pressed bar. In the manu¬ 
facture of cheap toilet soap—what is known in the trade as 
five-and-ten-cent goods—not only is material of inferior 
quality used, but also adulterants well known to the toilet- 
soap miller. A fragrant and lasting perfume may also be 
added. Palm oil forms an excellent ingredient of the toilet- 
soap base, the natural odor of the oil harmonizing well with 
the perfuming material. 


6 


MANUFACTURE OF SOAP, PART 3 


In the boiling of the toilet-soap base, the greatest care 
lies in completely saponifying the stock. In the use of 
coconut and cottonseed oils, this complete saponification is 
very important, for there are no oils used by the soap 
maker that are more liable to become rancid, especially when 
present as unsaponified stock in the finished soap, the rancidity 
being invariably betrayed by the odor on the hands after 
using. 


10. Boiling Toilet-Soap Base. —The manufacture of 
the toilet-soap base does not differ essentially from the manu¬ 
facture of settled rosin soap. Too much stress cannot be 
laid on the facts that the stock must be pure and fresh, 
the kettle and all appurtenances scrupulously clean, and that 
completeness of saponification must be insured. Covers for 
the kettles are usually provided in order to keep out dirt and 
to hold the heat for a longer settle. 

The stock change is effected as previously described, care 
being taken to kill the stock thoroughly, even though the 
stock lye may contain an excess of caustic alkali. A slight 
strength is desirable, as it is believed that the texture of the 
soap is improved thereby. After graining and settling 
the waste lye, the latter is run off. The soap is then boiled, 
or strengthened, with the addition of weak caustic lye, after 
which it is grained sharply with undiluted caustic lye. This 
strength lye is withdrawn and held in storage for use in 
inferior grades of soap. The soap is now boiled up with live 
steam, and water is carefully added until the soap shows a 
characteristic flat grain and is all but closed. The soap is 
now allowed to settle, as on the settling change in the manu¬ 
facture of settled rosin soap. 

11. The success of a toilet-soap settle can be determined 
by comparing the amount of water in the soap at the time of 
finishing with that of a 2- or 3-day settle. When the steam 
is shut off, a sample will show 40 to 47 per cent, of water; if 
the settle shows 30 to 31 per cent, of water, it will make good 
soap. Much variation from these figures will result in an 


MANUFACTURE OF SOAP, PART 3 


7 


unsatisfactory product when the soap is framed. It is 
believed that the more completely settled a toilet-soap base is, 
the better adapted it is for milling, due to the separation of 
salts and impurities that tend to form the niger. The more 
thoroughly these are removed, the less liable is the soap to 
come from the plodder in a cracked condition. At the expira¬ 
tion of the settling period, the soap, if no filler is added, is 
pumped directly into frames. 

12. The nature of the process to be used in the prepara¬ 
tion of the toilet-soap base and the care to be taken in the 
operation are determined by the quality of the product 
desired. For cheap, milled soaps, a base made by the cold 
process may be used, but more generally one made by the 
semiboiled process is used. With the latter process, the 
soap should be carefully settled; then the niger, if stock of 
good quality is used, can be incorporated in a succeeding 
boil or, preferably, added to a kettle charge for laundry 
soap. The soap is framed in the regular way and when cold 
is ready for cutting. 

In the manufacture of hard soap, free from filling, whether 
by the settled, the semiboiled, or the cold process, the yield 
is commonly estimated as 50 per cent. This, therefore, gives 
the toilet-soap base, by whatever process it is manufactured, 
a water content varying from 30 to 33 per cent. To insure a 
satisfactory product on milling, this percentage of water must 
be reduced about 50 per cent. With settled soap for laundry 
purposes, the water content was reduced from 3 to 5 per cent., 
just sufficient to permit a good finish on pressing and stamping. 

13. Preparation of the Toilet-Soap Base for Milling. 

In preparing the toilet-soap base for milling, the frame of soap 
is cut into long bars of such dimensions that the preliminary 
drying is effected in the quickest manner. At this stage it is 
merely desired to dry the soap, so that it can be reduced to 
chips in a cleanly manner. The superficially dried bars of 
soap are laid lengthwise in the feed-box a of the automatic 
chipper shown in Fig. 3, when they fall by gravity against the 


8 


MANUFACTURE OF SOAP, PART 3 


knives set in the radial slits b, two of which are shown. The 
soap can be cut into chips of any desired thickness by adjust¬ 
ing the knives at varying distances above the surface of the 
disk d , which is rotated by a pulley on the shaft c. The chips 

are collected on the 
opposite side of the 
machine and spread 
on the bottoms of 
trays. These are then 
transferred to the dry¬ 
ing room, where they 
are allowed to remain 
until the water con¬ 
tent has been reduced 
to that degree per¬ 
mitting the most 
satisfactory treatment 
in the milling machine. 

14. A very con¬ 
venient arrangement 
for the drying of 
toilet-soap chips is 
shown in Fig. 4. Air 
is forced over the soap 
contained in the trays of the case a, by means of the 
blower b, and escapes by means of the stack at one end. 
In the illustration the casing is partly broken away so as to 
show the location of the blower. The degree of dehydration 
is variable, depending on the quality of the product desired. 

If cheapening material is to be added in the mill, its capacity 
for moisture demands that the chips be not too dry, or the 
soap will come from the plodder in a cracked condition. Again, 
with unfilled toilet soap, the consistency of the mass may be 
varied at will by suitable treatment during the milling proc¬ 
ess. If the soap works too dry in the mill, either softer soap 
of the same quality or some water may be added,- according 
to the judgment of the miller. 






































MANUFACTURE OF SOAP, PART 3 


9 


The continuation of the drying process is best determined 
by experience. For goods of superior quality, the chips are 
sufficiently dry when the water content has been reduced 
from 30 or 33 per cent, to 15 or 18 per cent. The chips are 
now ready for the amalgamating and the milling processes. 

15. Amalgamator. —The amalgamator consists essen¬ 
tially of a rectangular box, set on a frame, and equipped with 
a horizontal shaft through the center of which are set paddles, 
as in the horizontal crutcher. It has for its object the mixing 
of the perfume and color with the dried soap before milling, 
and by its use one or two millings are saved. By the old 



method, the chips, color, and perfume were mixed in a box 
with a shovel. A very uniform mixture is possible with the 
amalgamator. 

16. Toilet-Soap Mill. —The toilet-soap mill, shown 
in Fig. 5, consists of a hopper a, in which the soap to be milled 
is placed, set on rolls b . and c of a series of granite rolls b , 
c, d, and e. These rolls vary from three to five in number. 
They are carried on heavy steel shafts, forming the core of the 
roll, and are mounted in the most improved machines one 
above the other at an angle of 45°. Granite, with a 
smooth and true finish, is generally used for the rolls, which 






















































10 


MANUFACTURE OF SOAP, PART 3 


vary in diameter from 8 to 18 inches, and in length from 
16 to 24 inches or longer, as desired. The capacity of the 
mill is rated by the manufacturer according to the amount of 
soap milled per hour, varying from 80 to 250 pounds for the 
roll dimensions just mentioned. The roll c, Fig. 5, is sup¬ 
ported in stationary journals. The intervening distances 
between adjoining rolls may be varied at will by means of 
setscrews on both sides of the mill. In the illustration, the 
setscrews on one side are shown at /, g, and h. The rolls 
rotate on their shafts in the directions indicated by the 
arrows. 



17. Milling the Toilet-Soap Base. —When the chips 
are dried suitably and have the right feel when taken up 
by the handful, the amount required for a charge is intro¬ 
duced into the hopper and passed through the mill until 
reduced to a fairly homogeneous mass. One milling should 
suffice for this initial reduction. 

During this preliminary milling, the distance between the 
rolls should be greater than at later stages in the milling proc¬ 
ess, owing to the coarseness of the material worked. During 
milling, the chips pass down between rolls b and c , Fig. 5, up 
between rolls c and d, and down between rolls d and e. Then, 






















MANUFACTURE OF SOAP, PART 3 


11 


in the condition of a thin, translucent film, they are removed 
by scrapers from the last roll and returned to the hopper, if 
desired, for another milling. 

18. When an amalgamator is not used, and the proper 
consistency has been reached by milling, the soap is collected 
in a box, or trough, where the perfume and coloring matter in 
proportions based on the weight of the charge of soap delivered 
to the mill is added. If the perfume and coloring matter are in 
a dry state, it may be simply dusted on the soap in the mill. 
If liquid, they must be added to the shreds of soap resulting 
from the first milling and allowed to percolate through, yet 
not flow from, the mass. The soap is then transferred to the 
hopper and worked through the mill to the satisfaction of the 
attendant. 

For cheap goods, three or four millings may suffice; for 
superior goods, or to produce the best possible texture in 
goods of any quality, seven or eight millings are required. 
After the milling process, the shreds of soap should be per¬ 
fectly homogeneous, with the perfume and coloring matter, 
if any of the latter is used, thoroughly worked through. 

19. Plodding Toilet Soap. —After satisfactory results 
have been obtained in the milling process, the soap is ready 
for the plodder. The soap as it comes from the mill is in thin, 
translucent laminae. The function of the plodder is to com¬ 
press this soap into a compact mass, which is expelled from 
the plodder in the form of an elongated bar. This bar is then 
cut into cakes of dimensions adapting them to the mold and 
die of the soap press. 

20. Plodders. —The earliest form of plodder consisted of 
the naked hands, which molded the mass and crudely kneaded 
it with mortar and pestle into a globular or oblong bar. 

The earliest form of machine plodder was a cylinder enclos¬ 
ing a screw, by means of which the soap that was fed into 
the cylinder at one end and above the screw was compressed. 
This is essentially the construction of the modern plodder. 
The improvements on this early form consist chiefly in 

394—10 


12 


MANUFACTURE OF SOAP, PART 3 


an increase and a more scientific distribution of the weight 
of the machine, and in the substitution of electricity as the 
source of power, thus permitting a greater compressive force 
to be applied to the soap. These mechanical improvements 
in the plodder have enabled toilet-soap manufacturers to 
produce a more compact, a more durable, and a better appear¬ 
ing piece of soap. 

21. In the plodder shown in Fig. 6, a is the hopper into 
which the soap is placed; b is the case enclosing the horizontal 



screw compressor impelled by power applied by means of a 
belt to the pulley c; d is a concentric hollow casing envelop¬ 
ing the nozzle of the plodder, and is filled with water added 
at g and maintained at a definite temperature. The cake 
former e is heated by a gas flame applied at /, and it is screwed 
to the nozzle through which the elongated bar of compressed 
soap is forced. A sectional connection h of the screw case 
provides for the ready examination of the interior of the case. 
So long as soap is added to the hopper, the action of the plodder 
is continuous. 




















































MANUFACTURE OF SOAP, PART 3 


13 


22. Plodders may be divided into two classes, according to 
the mode of applying the power, namely, the hydraulic and 
the motor-driven plodder. With the former, the output per 
day does not exceed 1,000 to 1,200 pounds of soap; with the 
latter, the output in the same length of time is much greater. 
The hydraulic plodder is being displaced by the motor-driven 
plodder, with its greater rapidity of operation. 

The nozzle of the plodder is provided with a screw head, 
to permit the attachment of the cake former. With this 
arrangement the elongated bar is made to assume any 



cross-section desired, as circular, square, or rectangular. 
The purpose of the hot-water jacket, shown at d, Fig. 6, is 
to soften the soap to such a consistency that, when forced 
through the cake former, the cohesion of the soap mass will 
not be destroyed and the soap will not, as it is termed, “crack” 
or “splinter.” Plodders are rated according to the pounds of 
soap capable of being plodded per day under a maximum 
average compressive force. 

23. Cutting and Pressing the Plodded Toilet Soap. 
The soap as it is delivered from the nozzle of the plodder is 



























14 


MANUFACTURE OF SOAP, PART 3 


carried to the cutting table, shown in Fig. 7. Here, the long 
bar is cut into separate cakes of uniform length by the wire a 
in the movable frame b operated by foot-power. The experi¬ 
ence of the attendant will determine at this stage whether it 
is necessary to subject the soap to a slight superficial drying 
in order to obtain the best possible impression on stamping. 
If the soap is sufficiently dry, it is taken from the cutting 



Fig. 8 

table in trays to the soap press. Formerly all milled soap was 
pressed on old-style foot presses, but power presses have been 
improved to such an extent that they are now used in the larger 
plants. From the press, the cakes are taken to the benches for 
hand wrapping, or to automatic wrapping machines. 

24. Continuous Crusher and Dryer. —The patented 
process known as the continuous crusher and dryer 













































































































































MANUFACTURE OF SOAP, PART 3 


15 


possesses the double advantage of shortening the time of 
manufacture and of very materially decreasing the cost of 
production. In this process, instead of slowly cooling great 
masses of soap in bulk, the paste is treated while still hot 
and in a liquid state, just as it comes from the kettle. While 
available for household and industrial soaps, this process 
is used almost exclusively for toilet soaps. 

In the manufacture of toilet soap by the usual process, as 
previously explained, the material is taken from the kettle, 
crushed, framed, slabbed, caked, and chipped before passing 
to the drying room. By this special process, however, the 
hot soap passes directly from the kettle to the machine in 
which the drying is to take place, the only intermediate step 
being the pumping of the soap from the soap vat to the 
storage tank. This is done in order to elevate the soap above 
the crusher and dryer and to regulate its flow into the hopper a, 
Figs. 8 and 9. 

The mixing tank b, Fig. 9, is discarded by most users of 
the machine, the color and perfume being added to the dry 
and cold soap in the mixer /. 

25. A boiled settled soap is usually crushed while at a tem¬ 
perature of from 65° C. to 70° C., but soap can be pumped 
to this machine at a temperature of 80° C. The soap paste 
passes from the hopper to the first roller c, Fig. 9, of the five 
horizontal rollers c to c"". The speed and pressure of these 
rollers gradually increase in the order in which they are 
lettered, being greatest at roller c"". The soap paste strik¬ 
ing the rollers curdles at once and gets crushed into thin layers, 
which a knife divides into ribbons. The soap leaves the 
rollers c"" as a thin ribbon, or film, and falls on an endless 
band of wire gauze circulating in the drying chamber. These 
bands are shown through the open doors in the side of the appa¬ 
ratus, Fig. 8. The time required for the soap to pass from the 
hopper through the dryer to the box d, Fig. 9, is only about 
12 minutes, during which period it travels the full length 
of the dryer a number of times, falling from one wire band 
to another. 


fan Blower 


^ <0 

«|4 


1\, 



/ 


cdcs'sjj 


\ 


r 


S-JVff 


J9PPO/J 


0 \ 

6 

M 


Ssks w. 


16 
















































































































MANUFACTURE OF SOAP, PART 3 


17 


The dryer is heated by the steam coil e, Fig. 8, and the hot 
and moist air passes away through the pipe d. The tempera¬ 
ture maintained in the dryer is about 35° C., as this has been 
found to give the best results. 

These machines are constructed in various sizes, and their 
output ranges from 250 to 800 pounds per hour. 


PERFUMING OF SOAP 


PURPOSE OF PERFUMING 

26. Competition in the toilet-soap business has reduced 
the profit to a very small margin. One important charac¬ 
teristic of this business is the manner in which the goods 
are put on the market. An attractive wrapper and an agree¬ 
able perfume are demanded by the inexperienced buyer of 
this class of soap to the exclusion of the essential qualities. 
By means of coloring matter and suitably blended essential 
oils, a milled soap made from very inferior stock may have 
its original inferiority completely obscured. 

27. The blending of essential oils is a recognized art, whose 
development requires the constant attention and study of the 
skilled perfumer. The demand is always for something new, 
to supply which the toilet-soap manufacturer is often hard 
pressed. Organic chemistry has supplied the perfumer with 
a large and increasing number of artificial perfumes, which 
often surpass the natural source in intensity of fragrance and 
cheapness. Some of these, as nitrobenzene, or oil of mir- 
bane, a cheap and efficient substitute for the oil of bitter 
almonds for perfuming laundry soap, are obtained from coal 
tar; others, as vanillin, borneol, menthol, eugenol, ionone, 
heliotropin, etc., are prepared synthetically; certain others are 
isolated from essential oils, as safrol, from oil of camphor, 
which has practically displaced the natural oil of sassafras as 
a soap perfume; citral, from oil of lemon; carvol. from oil of 
caraway; etc. 




18 


MANUFACTURE OF SOAP, PART 3 


PERFUMES USED IN LAUNDRY SOAPS 

28. The following list of essential oils comprises those 
most commonly used for perfuming laundry soap. As has 
been noted, the proportion used seldom exceeds 2§ pounds 
per frame of 1,200 pounds of soap. 

Oil of caraway seed. 

Oil of cassia, with guaranteed percentage of cinnamic 
aldehyde. 

Oil of cedarwood. 

Oil of citronella. 

Oil of mirbane, artificial, with odor of oil of bitter almonds. 

Oil of rosemary: 

Safrol, artificial oil of sassafras. 

Oil of eucalyptus 

Oil of thyme. 

29. The best way to ascertain the most satisfactory com¬ 
bination of essentials oils for a laundry-soap perfume is to 
prepare a number of mixtures to be used experimentally as a 


TABLE I 

FORMULAS FOR PERFUMING OF LAUNDRY SOAP 


Essential Oils 

Formula 1 

Parts by Weights 

Formula 2 
Parts by Weights 

Safrol. 

23 

27 

Cedarwood . 

12 

10 

Cassia. 

9 

7 

Lavender . 

10 

10 


basis, or vehicle, for a highly fragrant and strong-bodied 
essential oil, as artificial oil of sassafras, or safrol. This 
particular oil commends itself because of its cheapness. Its 
fragrance may be modified by mixing it in varying proportions 
with other essential oils, not debarred by their high cost, until 
a mixture is obtained that is at once cheap, lasting in fra¬ 
grance, and disguises most completely and agreeably the 
odor associated with the soap in use. 

















MANUFACTURE OF SOAP, PART 3 


19 


After two or three mixtures of equal satisfaction are 
obtained experimentally, the mixtures may be subjected 
to practical tests by studying results when they are mixed 
in regulated proportions in successive frames of soap. 

The formulas in Table I represent two mixtures, No. 2 
being modified from No. 1 as the result of an advance in 
the price of cassia oil. Equally satisfactory results were 
obtained from both mixtures. 

30. Laundry soap is seldom colored, indigo paste being the 
only color that is used to any great extent. The blue soap 
thus produced often misleads the consumer into the idea 
that bluing is being added at the same time that washing 
is being done. Unbleached palm oil is the cheapest and 
most efficient available agent to disguise the odor and color 
of rosin. Very small quantities of ultramarine are used 
in some cases to heighten the whiteness of floating soaps. 
Disinfectant and tar soaps are colored, the former variably, 
the latter with pine tar. 


PERFUMING OF TOILET SOAP 

31. The direct application of the perfuming material to 
the mass of thin, shredded soap, after its preliminary treat¬ 
ment in the mill to obtain homogeneity, involves no especial 
difficulty. A weighed or measured quantity of perfume is 
simply added to the mass in the box in which the shredded 
soap accumulates as received from the mill, and the perfume 
is then incorporated sufficiently with the soap to enable the 
attendant to transfer it to the hopper of the mill without waste. 

The blending of perfuming material to obtain desired 
odors, generally those imitating the natural odors of fresh 
flowers, constitutes a distinct art and requires for profi¬ 
ciency an intimate knowledge of the chemistry of essential 
oils and experience in working with them. The various 
ingredients of the perfumed stock may be bought separately 
and then compounded or blended by the perfumer, or they 
may be bought already blended from dealers in essential oils 
and perfumers’ materials. 



20 


MANUFACTURE OF SOAP, PART 3 


32. With -the exception of musk and civet, which are 
excretory secretions of the animals producing them, the raw 
materials of soap perfumery consist chiefly of essential oils 
obtained from wood, as oil of cedarwood; from bark, as the 
oil of wild cherry; from foliage, as oil of eucalyptus; from fruit 
or seed, as oil of caraway; and from flowers, the chief source, 
as oil of rosemary. 

There is a large and increasing number of synthetic prep¬ 
arations and isolated bodies possessing in a marked degree 
the fragrance of the natural source that now successfully 
compete with the latter. These bodies, as a rule, are the 
odoriferous principle of the natural oil, and for purposes of 
perfumery are not encumbered with the non-essential ingre¬ 
dients present in the natural oil. A correspondingly smaller 
quantity can be used to effect the same results and thus 
generally reduce the cost of production. 

33. The fractional distillation of essential oils obtained 
from plants has shown that they are composed of a nearly 
odorless vehicle, consisting of one or more hydrocarbons of 
the terpene class, a principal odorous constituent, which may 
be an alcohol, phenol, aldehyde, ketone, ether, or ester, and 
smaller quantities of various other compounds. These mod¬ 
ifying constituents may vary in amount in oil obtained from 
different parts of the same plant. 


COLORING OF TOILET SOAP 

34. The operation of coloring is carried out in the amalga¬ 
mator, in which the coloring matter, either dry or in solution, 
may be added to the soap. If an amalgamator is not used, 
the coloring matter may be added to the soap in the mill hopper 
or it may be spread out on the thin layer of soap as it passes on 
to the rolls of the mill. If it is deemed desirable, it may also 
be added directly to the soap in the box at the end of the mill 
after thfe soap has had a preliminary milling. 

The application of the coloring material in solution is pref¬ 
erable to using material in the dry state, as it admits of a 



MANUFACTURE OF SOAP, PART 3 


21 


more homogeneous distribution of the color in the shortest time. 
There should be a consistency between the nature of the 
coloring material used, the odor of the perfume, the character 
of the soap, and the name applied to it. 

35. The organic coloring materials commonly used are 
obtained from coal tar and receive trade names that give no 
indication of their composition to the purchaser. Red, pink, 

TABLE II 


COLORS USED IN SOAP AND CHIEF MATERIALS FOR 

PRODUCING THEM 


Color 

Material 

Red. 

Coal-tar colors: vermilion, Venetian 
red, alkanet, bole, colcothar, cinna¬ 
bar, chrome red, carmine. 

Orange and yellow . . . 

Coal-tar colors: chrome yellow, cad¬ 
mium yellow, curcumin, gamboge, 
turmeric. 

Green. 

Coal-tar colors: ultramarine green, 
chlorophyl extract. 

Brown. 

Coal-tar colors: brown oxides of iron, 
mixed blue and yellow colors. 

Blue and lilac. 

Coal-tar color: ultramarine blue. 


orange, yellow, green, brown, blue, and lilac colors are obtained 
direct from the makers or already compounded from dealers 
in perfumers’ materials and with guaranteed solubility in 
definite parts of hot or cold water. The primary qualifications 
of a soap dye are inertness to the action of alkali and per¬ 
manency under the conditions in which the soap is used. 

In Table II are given the chief materials used for producing 
various colors used in the coloring of toilet soap. 





















22 


MANUFACTURE OF SOAP, PART 3 


The intensity of the color is determined by the amount of 
dye used and the character of the soap. Coconut oil, for 
instance, as an ingredient of a toilet-soap base will permit of 
greater brilliancy than would be possible without its use. 


MANUFACTURE OF SOAP POWDER 

36. The manufacture of soap powder in recent years 
has grown into a business of considerable magnitude. The 
earliest of those engaged in its manufacture found the busi¬ 
ness extremely profitable, but with growing competition the 
margin has been considerably reduced. Well-made, settled, 
resinous soap can be filled with upwards of 10 per cent, of 
soda-ash solution with good results. If this filling is increased 
in quantity until present in the mixture greatly in excess of the 
soap, a compound results which, when reduced to a finely 
divided state, constitutes the soap or washing powder of trade. 
The first consideration in the manufacture of soap powder is 
the composition of the soap base. Any glyceride soap stock 
is available for this purpose. A good soap-powder soap can 
also be made by using corn or cottonseed oil and grease. 

Rosin, which forms a soft, sticky soap, with great affinity 
for water, resulting in the formation of lumps in the powder, 
should not be used, or at best only in small proportion and in 
combination with a firm tallow base. The prime requisites of a 
soap powder are freedom from lumps, quick solubility, and 
uniformity of size of the particles composing it. Some soap 
powders are more finely divided than others, the degree of 
pulverization being determined by either the fancy of the 
manufacturer or the demand of the trade. 

37. All soap powders are mixtures of soap, soda ash, and 
water, and vary only in the percentages of these ingredients and 
the kind of soap used in their preparation. They are divided 
into two classes, depending upon the amount of water present, 
and are called old style and fluffy. The old style contains 10 to 
20 per cent, of water and the fluffy 30 to 40 per cent. Typical 



MANUFACTURE OF SOAP, PART 3 


23 


analyses are given in Table III. With the old-style powder 
the lumps are coarse and harder because sufficient water is 
not present to form sal soda {NchCOz-10H 2 O) with all of the 
soda ash (Aa 2 C0 3 ) present. For this reason considerable heat 
is felt when wet hands come in contact with it. This is its 
chief objection. The fluffy powder contains sufficient water 
to form sal soda with all of its soda ash and is soft to the touch. 
It occupies considerably more space than the old-style powder. 

38. Manufacture of Old-Style Powder. —In the manu¬ 
facture of old-style powder, the soda ash, soap, and hot water 
are dumped into a mixer of the horizontal crutcher type and 
mixed until the product is lumpy. A mixer charge is usually 


TABLE III 

ANALYSES OF SOAP POWDERS 



Old Style 

Fluffy 


1 

2 

3 

4 

5 

Moisture . 

13.33 

14.30 

34.66 

37.92 

40.30 

Dry soap . 

15.12 

27.80 

23.47 

30.15 

20.61 

Sodium carbonate . 

71.55 

57.90 

41.87 

31.93 

39.09 


based on the bag of soda ash, which weighs 300 pounds, as a 
unit. The lumpy material is then discharged from the mixer 
and raked through screens to break it up and to cool it as 
much as possible. It is then shoveled onto trays that have high 
sides. These trays are then piled up in a well-ventilated room. 
About 5 hours is required to set the powder under the best 
conditions. It is then ready for milling. 

39. Manufacture of Fluffy Powder. —Fluffy soap 
powder is made by a continuous process. The material as 
it comes from the mixer falls upon a series of hollow rolls 
through which cold brine circulates. The rolls are arranged 
one above the other so that the thin layer of powder which is 
scraped from the upper roll, after it has made one revolution, 



















24 


MANUFACTURE OF SOAP, PART 3 


falls on the second roll, and so on until the powder is cold and 
crystallization is complete. The powder is then put through a 
screen, weighed, and packed. 

40. Soap Base. —As a soap base, any settled or semi- 
boiled non-resinous soap may be employed. If corn or cotton¬ 
seed oil is used, the soap, after saponification, is grained with 
caustic-soda lye, which is later drawn to a kettle that is tak¬ 
ing a stock change for a settled soap. The alkaline strength 
is then used up in saponifying part of this stock. If circum¬ 
stances do not warrant the separation of glycerine by graining 
the soap, a semiboiled soap composed of simple ingredients 
will satisfy every requirement. 

41. Soap-Powder Mill. —The soap-powder mill is of 
especial importance in the manufacture of soap powder, and 



should be so constructed as to do the work quickly, without 
heating the powder, and with a minimum of dust and repairs. 
The machine shown in Fig. 10 receives the trays of coarse soap 
powder, previously broken into lumps, in a hopper attached 
to the collar a, and crushes, grinds, and sifts it in one 
continuous automatic operation. The lumps are reduced by 
repeated blows of rapidly revolving steel blades, or beaters, 
enclosed in the semicylindrical casing shown at b. The 
powder is discharged through a semicylindrical screen, which 
serves as a sifter and which forms the under side of the casing b. 
Power is applied by belt at c. The mill is mounted on a 
well-braced framework that is completely enclosed to retain 





















MANUFACTURE OF SOAP, PART 3 


25 


dust and high enough to admit the introduction of a barrel to 
receive the powdered material. A newer style of mill employs 
the same principle on a larger scale, but is equipped with much 
greater screening surface. 

42. The soap-powder department is usually arranged so 
that the mixers are on one floor, the mills on the door below, 
and the weighing, filling, and sealing machines on the next 
floor below the mills. The weighing, filling, and sealing are 
all done automatically on special machines of which there are 
several types. The operations connected with soap powder 
making are very disagreeable because of the dust. All 
machines should be provided with hoods that have very strong 
exhausts. 

43. Scouring Powder. —Scouring powder is also a soap- 
factory product. It is a mixture of soap powder, grit, and 
talc, with, at times, sal ammoniac. It requires no milling as 
all the ingredients are purchased in the powdered state. These 
are mixed, delivered by the conveyer to the weighing machines, 
filled and sealed into the cans or cartons. The various brands 
on the market differ in the amounts of their ingredients and 
in the kind of grit used. 

RECOVERY OF GLYCERINE FROM 
WASTE-SOAP LYE 


MANUFACTURE OF GLYCERINE 

44. Historical. —Scheele, in 1779, when preparing lead 
plaster by heating olive oil with litharge, obtained a soluble, 
sweet-tasting substance, and later, in 1784, he found that the 
same substance could be obtained from other oils, as well as 
from butter and lard. To this material he gave the name 
the sweet principle of fats , and it afterwards bore the name 
of Scheele’s sweet principle, or oil sugar. 

Lead plaster is said to have been discovered by the Roman 
physician Menecrates about the middle of the 1st century, 
and also to have been known to Pliny, who briefly described 




26 


MANUFACTURE OF SOAP, PART 3 


its uses, mode of preparation, and application, but nothing 
was known of glycerine until Scheele’s day. 

Later, the body was more carefully investigated by Chevreul, 
who determined its composition with tolerable exactitude 
and gave to it the name that it now bears. Pilouze in 1836 
first established its formula. His experimental results 
corroborated Chevreul’s views that the fats are ether-like 
compounds of the fatty acids. Henceforth glycerine became 
the subject of study by Berzelius, Liebig, Berthelot, and de 
Luca; but it remained for Wurtz to determine its exact 
chemical composition and relation to other bodies of the ali¬ 
phatic series. 

45. Scheele published the results of his investigations in a 
communication that appeared in the Transactions of the 
Royal Academy of Sweden, in 1783. He describes his 
method of preparation in the following terms: “It is not 
generally known that all solid oils obtained by pressure con¬ 
tain a natural sweet principle which differs in its special 
relations and properties from the other well-known saccharine 
materials occurring in the vegetable kingdom. This sweet 
principle makes its appearance when oils of this kind are 
boiled with litharge and water until the whole of the litharge 
is dissolved by the oil. Water is then poured upon the 
emplastrum simplex thus formed, the whole boiled for a 
few minutes, and on cooling the liquid is filtered off from 
the plaster and boiled until the residue becomes sirupy.” 

46. Glycerine was prepared by the foregoing process 
alone for many years, the lead introduced as an impurity 
from the litharge being removed, before concentrating the 
filtrate, by the use of hydrogen sulphide. This concentrated 
filtrate, after some primitive clarification, constituted the 
glycerine of commerce. Its rapidly increasing use soon 
demanded its production on a larger scale. It was known 
that in the process of soap making the glycerine liberated 
from the fat in the act of saponification remained in the waste 
lye, but efforts to recover it from this medium with the 
extremely crude methods used were unsuccessful. 


MANUFACTURE OF SOAP, PART 3 


27 


In the meantime the manufacture of stearin candles was 
undergoing important developments. Numerous patents 
were granted for processes for the decomposition of the fats 
and the separation of glycerine. Gay-Lussac and Chevreul, 
in 1825, were the first to obtain patents. Their patent was 
for the alkaline saponification process, which, however, did 
not admit of successful operation until after the improve¬ 
ment by de Milly, in 1831. This is the autoclave process at 
present in use. 

47. During the succeeding 20 years the sulphuric-acid 
distillation process was proposed and developed. Although 
other investigators had worked with the problem, and in fact a 
form of the process was in actual use, it remained for an 
American chemist, R. A. Tilghman, to determine the condi¬ 
tions productive of the most successful results. For his 
originality he received a patent in 1854. An English patent 
was soon after taken out. Tilghman’s process is the one at 
present employed in conjunction with the use of sulphuric 
acid. 


48. In 1847, Sobrero, in Paris, discovered nitroglycerine. 
Alfred Nobel demonstrated its value as an explosive in 1863 
and in 1866 invented dynamite. This was followed in 1875 
by blasting gelatin. The construction of vast engineering 
undertakings was greatly facilitated by the use of these sub¬ 
stances, of which glycerine is the basis. The increased use 
of glycerine reacted directly on the source of the raw material, 
and the soap trade soon came to a perplexing realization of 
the increasing value of the product that was being daily con¬ 
signed to the sewer. 

49. Treatment of Waste Lye. —In the discussion of 
the manufacture of settled resinous soap, the progress of a 
boil of soap was traced, showing the formation of the various 
lyes. These are dilute solutions of varying percentages of 
sodium hydroxide, sodium carbonate, sodium sulphate, sodium 
chloride, and glycerine, and are contaminated by more or 
less soap in suspension, together with coloring matter intro- 


394—11 


28 


MANUFACTURE OF SOAP, PART 3 


duced by the rosin and with some mucilaginous matter or 
animal tissue remaining in the stock when rendered. This 
liquor, which often has a foul odor and is a by-product with 
the soap maker, now becomes the raw material of the glycerine 
refiner. 

50. The process and apparatus used represent the 
culmination, in efficiency and simplicity, of all systems of 
glycerine recovery from waste lye. It has been declared 
impossible to prepare a chemically pure glycerine from waste 
lye—that glycerine of dynamite grade represents the limit in 
purity of glycerine obtained from this source. Soap lye, 
by the improved treatment at present in use, is made to yield 
a glycerine of the highest purity and answering the severest 
requirement of any pharmacopoeia. In the processes that 
have received the substantial approval of general practical use, 
the agents employed for the precipitation of albuminous and 
soapy matter and the neutralization of the alkali present in 
the lye are sulphuric acid, hydrochloric acid, alum, and a basic 
sulphate of iron. 

51. The basic sulphate of iron is prepared by treating 
pulverized iron ore with sulphuric acid, whereby an acid 
salt mixed with some uncombined ore and acid is obtained. 
This mixture is subsequently subjected to a high temperature, 
namely, 380° to 500° F., when it undergoes a transformation 
into a basic sulphate of iron. The efficiency of basic sulphate 
of iron as a clarifying agent depends on the formation of ferric 
hydrate and insoluble iron soaps that entangle completely 
the albuminous matters, all of which in settling through the 
liquor clarify and decolorize it. 

52. The waste lyes from the stock and wash changes are run 
into storage tanks situated in a convenient place below the 
soap kettles and above the treatment tanks so as to save 
pumping. Before they can be evaporated, the alkali must be 
neutralized to prevent frothing when boiled. The treatment 
also removes the mucilage and tissue. There are two general 
methods, one of which is a patented process that uses the 


MANUFACTURE OF SOAP, PART 3 


29 


basic sulphate of iron previously described. The other one 
neutralizes about three-quarters of the alkalinity with hydro¬ 
chloric acid, and the remainder with alum. The precipitated 
iron hydroxide in the first method and the aluminum hydrox¬ 
ide in the second do the coagulating and clarifying. In any 
treatment used, the lye is left after treatment very slightly 
alkaline, usually about .02 per cent. 

53. Basic Sulphate-of-Iron Method. —The waste lye 
is run into the treatment tank and stirred with compressed air. 
A sample is taken and its alkalinity determined. The amount 
of basic sulphate of iron needed is dumped into the tank and the 
air turned on to keep it well agitated. In 20 minutes a sample 
is taken, filtered, and the alkalinity again determined. When 
the alkalinity is correct, the tank is emptied by pumping 
through a filter press into another storage tank from which 
the evaporators are fed. 

54. Hydrochloric Acid and Alum Treatment. —The 

procedure is the same as that just described, except that three- 
quarters of the alkalinity is neutralized with hydrochloric acid 
and the remainder with alum. The operators in the glycerine 
plant are given tables by which the amounts of these chemicals 
needed for the alkali content are read off directly. 

The entire glycerine recovery is controlled by a few simple 
chemical tests and the solutions and apparatus needed are 
placed in the glycerine-plant office. The use of these is 
taught to the men operating the treatment tanks, evaporators, 
and stills, so that the routine control work is taken out of the 
main laboratory, which is then concerned only with the more 
difficult work of testing the finished glycerine. 

55. Evaporation of Treated Lye. —The next step is to 
remove the water and salt and concentrate the glycerine into 
what is known as crude. The crude contains from 77 to 85 
per cent, of glycerine. This is done in an evaporator especially 
designed for the work. The evaporators are built in single or 
multiple effects. By multiple effects is meant, that the steam 
chest of the second effect receives its steam from the vapor 



Fig. 11 


3C 


















































































MANUFACTURE OF SOAP, PART 3 


31 


line of the first effect. These evaporators are operated under 
a high vacuum, say 27 to 28 inches. 

The evaporator shown in Fig. 11 is of the single-effect type. 
The process is the same with any number of effects, and for 
descriptive purposes the single effect is less confusing. It 
is a large tank built of steel plates. A steam chest a consisting 
of numerous small tubes to allow the circulation of the boiling 
liquor, and two or three larger tubes to increase this circulation, 
is built into the lower part of the evaporator. This arrange¬ 
ment also allows the salt, which is thrown out of solution as the 
concentration increases, an easy means of passing down into 
the salt drum b. The small drums c are placed at the top of 
the evaporator and fitted with baffles d to catch any entrained 
liquor and to return it by the line e to the evaporator. The 
vapors are removed by the line /, which is also connected with 
the pump which maintains the vacuum. 

56. The treated lye is fed into the evaporator through the 
line g, Fig. 11. The steam chest is supplied with steam 
through the line h. For all light liquors, the boiling is done 
with exhaust steam, and, as it gets heavier, live steam must 
be used. The condensation is removed by the drip j. The 
height of the lye in the evaporator is controlled by the sight 
glass k , which is usually fitted with two bands to marktheupper 
and lower levels to be carried. The condensation in the steam 
chest is noted by the sight glass /, while w is a plate-glass 
window through which the boiling can be observed. 

The bottom of the evaporator is fitted with a flange on 
which a large valve m is bolted, and below this valve is hung 
the salt drum b. A tank o is placed under the salt^drum to 
catch and dry the recovered salt. This tank has a false 
bottom r which is connected with a pump p for drawing off as 
much lye as possible from the salt. The salt drum is provided 
with a vacuum line t. At some convenient place on the lower 
part of the evaporator handy for operation, a draw-off con¬ 
nection 5 is fitted for sampling. Fig. 11 (a) is a plan view of 
the top and bottom tube sheets of the steam chest, and ( b ) is a 
side elevation of the evaporator, showing the pitch of the salt 


32 


MANUFACTURE OF SOAP, PART 3 


drum. The entire evaporator and lines are heavily insulated 
to conserve the heat. 

57. Operation of Evaporators. —All the valves of the 
evaporator, Fig. 11, are closed except j and m, and that on 
the line /. A vacuum of 27 to 28 inches, or the capacity of 
the pump, is drawn and maintained. The valve on the line g 
is opened and lye drawn to the upper mark on the glass k. 
Steam is turned into the steam chest and the boiling continued 
with fresh additions of the lye as it boils down. With soap 
lyes containing between 3 and 4 per cent, of glycerine and 
varying amounts of salt, not much change is noticed for a few 
hours, but as the concentration of glycerine progresses, the salt 
is precipitated and in set tling forces the lye out of the salt drum b. 
When the evaporation has continued for several hours, 
the valve m is closed, the vent x opened slowly to break the 
vacuum, and the door y is opened to drop the salt into the 
tank o. Some of the salt will run out, but most of it must be 
removed with a hoe. The boiling is not interrupted. The 
door facings are washed with water to make a perfect joint; 
this door y and the vent x are closed. A vacuum is drawn 
on the salt drum b through the pipe t, and when the vacuum 
of the drum equals that of the evaporator, the salt valve m 
is opened slowly, and the boiling-down process continued. 
This may be finished as a crude of 75 to 85 per cent, of glycer¬ 
ine, which is discharged to tanks through the pipe z. This 
crude has a specific gravity of about 33° Be. 

It is here that practice varies. The evaporators are 
usually made up of several units and are put on a schedule 
of salt drops and lye drops that are staggered in time, so as to 
keep the work continuous. The evaporation is carried to a 
half crude as one step and finished to crude as the second. 

Smaller evaporators are used for the second step. Table IV 
shows to what extent the glycerine content of the liquor is 
increased, and the salt and sodium sulphate content is 
decreased, by evaporation. 

To save as much heavy lye as possible and also to facilitate 
handling back to the soap kettles, the salt is made very dry 


MANUFACTURE OF SOAP, PART 3 


33 


by the pump on the line p. At some factories the drying is 
done in centrifugals. Thus far the main object has been to 


TABLE IV 
EVAPORATOR LIQUORS 


Degrees 

Baume 

Glycerine 
Per Cent. 

Salt 

Per Cent. 

Sodium 

Sulphate 

Per Cent. 

Boiling 

Point 

Degrees C. 

27.9 

19.00 

19.73 

3.51 

109 

27.8 

23.44 

18.86 

2.33 

109 

28.0 

29.44 

17.34 

1.78 

112 

28.3 

35.21 

16.29 

1.29 

111 

28.7 

43.68 

14.32 

.82 

113 

29.5 

56.17 

12.52 

.80 

116. 

33.4 

81.90 

6.82 

.51 

162 

33.8 

81.75 

7.08 

.22 

167 


remove, as far as possible, all water and salt from the lye and 
concentrate the glycerine in the crude. 


TREATMENT OF CRUDE GLYCERINE 

58. Crude Glycerine. —Crude glycerine contains from 
75 to 85 per cent, of glycerol, about 6 per cent, of salts, chiefly 
sodium chloride, about 5 per cent, of organic matter, constitut¬ 
ing the foots obtained on subsequent distillation, while the 
remainder is water. It is a thick, viscous liquid, its color and 
clearness depending in a great measure on the character of the 
stock and the efficiency of the preliminary treatment that the 
fresh lyes have received for the removal of organic matter, 
including iron salts of the organic acids. 

59. Distillation of Crude Glycerine. —The crude 
glycerine is withdrawn into storage tanks, from which it is 
transferred, as required, to another vacuum apparatus in 
which the dillation is conducted. This apparatus comprises 
a large cylindrical sheet-iron tank, in which the crude glyc- 















34 


MANUFACTURE OF SOAP, PART 3 


erine is distilled, and a series of vertical pipes terminating 
at the bottoms in horizontal cylindrical reservoirs, in which 
the distillate condensed in the vertical pipes collects. These 
reservoirs are termed catch-alls. A still 3 feet 6 inches in 
diameter and 6 feet high will have about seven catch-alls 
which may vary from 18 inches near the still, to 30 inches in 
diameter at the end of the system, all being about 5 feet 
6 inches long. These catch-alls are in reality air condensers. 

60 . At the end of the series of catch-alls are two larger 
horizontal cylindrical vessels surmounted by an iron cylinder 
filled with water-cooled tubes, through which the more volatile 
portion of the distillate passes and is condensed, falling into 
the reservoirs below. These vessels, called sweet-water 
drums , communicate with a dry-air vacuum pump, which 
maintains a vacuum of about 28.5 inches throughout the 
system. Steam at a pressure of 125 pounds, corresponding to 
a temperature of 345° F., circulates in a closed coil and main¬ 
tains a constant temperature. 

61 . Advantage of System. —The essential advantage 
of this system of glycerine distillation consists in the injec¬ 
tion of expanded and reheated steam into the body of crude 
glycerine maintained at a high temperature. Glycerine has 
a boiling point of 290° C., or 554° F. Under atmospheric 
pressure, however, it cannot be heated to this temperature 
without undergoing decomposition. By reducing the pres¬ 
sure, as is done in a closed vessel when a vacuum is maintained, 
it boils without decomposition, and its vapor may be con¬ 
densed unchanged. Commercial crude glycerine is very 
impure, the organic matter present causing difficulty in the 
refining process. To separate this organic matter effectually, 
recourse must be had to some means other than boiling at a 
lower temperature under reduced pressure. To accomplish 
this, a jet of expanded and reheated steam is introduced into 
the mass of crude glycerine heated to the temperature of 
distillation. 

62. If steam at boiler pressure, namely, 125 pounds, were 
used directly for distillation without being previously expanded 


MANUFACTURE OF SOAP, PART 3 


35 


and reheated, its expansion in the distilling apparatus would 
not only greatly retard, but would practically stop, the opera¬ 
tion. To the great loss in heat due to absorption by the 
expanded steam would be added the difficulty arising from 
its condensation. These adverse and prohibitory conditions 
are eliminated by the use of expanded and reheated steam, 
which is prepared in the following manner: Steam taken 
directly from the boilers is allowed to expand in a coiled 
pipe of larger diameter located inside of a well-insulated 
vessel, called a reheater , which is attached to each still and in 
many cases is larger than the still itself. 

63 . The steam in expanding suffers a reduction in tem¬ 
perature. The heat lost is restored by surrounding the coil 
within the reheater with the same unexpanded steam from the 
boiler. Steam thus treated is introduced directly into the 
crude glycerine, which distils without decomposition at a 
temperature of about 300° F. Before introducing the steam, 
crude glycerine is added in sufficient quantity to cover the 
jet pipe to a satisfactory height, as indicated by the gauge glass, 
and as the distillation continues, crude glycerine is added from 
time to time in quantities not too great to interfere with the 
even working of the still, never, however, allowing it to fall 
below the established level. If, from lack of attention on 
the part of the attendant, an excessive quantity is introduced, 
there is great danger of the entrainment of the impurities 
contained in the crude glycerine, which increase in quantity 
in the still as the distillation proceeds. 

64 . Crude-Glycerine Still. —In the still shown in 
Fig. 12, A is the still proper, B the reheater, C andC' the catch¬ 
all drums, and D the sweet-water drum. In the still A, 
the closed coil, shown in dotted lines, carries steam at boiler 
pressure, which heats the contents of the still to the tempera¬ 
ture required for distillation. In the reheater B , steam at a 
pressure of 125 pounds enters through the pipe a and expands 
into the coil of larger diameter, which is shown in dotted lines. 
This expansion coil is surrounded by steam at boiler pressure 
entering the reheater through the pipe 6, which also carries 



36 


Fig. 12 











































































































































































MANUFACTURE OF SOAP, PART 3 


37 


steam at the same pressure into the heating coil of the still A. 
Expanded and reheated steam from the reheater enters the still 
through the pipe c and discharges into the crude glycerine 
contained therein through the crisscross jet shown at d. The 
catch-all stuff, so called, collects in the catch-all drums C 
and C', and the lighter portion of the distillate condensed in 
the water-cooled jacket at E collects in the sweet-water 
drum D. At e, e ', and e" are outlets for the water of con¬ 
densation from, respectively, the reheater B , the high- 
pressure steam line from the boiler, and the heating coil of 
the still A. At /, crude glycerine is fed into the still by suction. 
At g is the drop door through which the foots in the still A 
is discharged. Water used for washing the still is discharged 
at h. The level of the contents, of the still is shown by the 
gauge glass i. At j and k are the discharge valves for the 
contents, respectively, of the catch-all drums C and C' and 
the sweet-water drum D. Tanks / and m are reservoirs for 
these respective portions of the distillate. All steam pipes 
leading to and from the apparatus, as well as the still and 
reheater, are insulated so as to retain the heat. 

Before beginning a distillation, it is customary to have in 
stock a considerable quantity of crude glycerine, so that 
there will arise no necessity of shutting down the apparatus 
before conditions in the still render it imperative. Fresh 
lye is undergoing concentration all the time, and naturally 
the product of one operation comes in greatly reduced bulk 
to be the raw material of the next. 

65. Tests During Distillation. —One of the chemical 
requirements of a dynamite glycerine is that it should not 
contain over .01 per cent, of salt. The best indication that a 
still has boiled over, that is, that some of the crude has been 
mechanically carried over to the catch-alls, is the presence 
of a high chlorine content in the distillate. It is possible to 
ascertain the amount of chlorine and control this part of the 
operation by providing the attendant with a simple chemical 
test and teaching him its use. All the catch-alls are fitted 
with sampling pipes. A large sample, say 50 to 100 cubic 


38 


MANUFACTURE OF SOAP, PART 3 


centimeters, is obtained, a few drops of potassium-chromate 
solution added, the mixture diluted with distilled water, and 
titrated with a standard solution of silver nitrate, drop by drop, 
until the permanent silver chromate precipitate is formed. 
This silver-nitrate solution is of such strength that either 10 or 
20 drops indicate the limit of salt allowed. The test is most 
valuable. The distillation runs a long time before dropping, 
say 24 to 36 hours, and it is very essential that the purity of the 
distillate should be known at all times. The controlling test 


TABLE V 

GLYCERINE DISTILLATES 


Catch-All 

Specific 
Gravity 
at 15.5° C. 

Chlorine 

Per Cent. 

First . 

1.2595 

.0011 

Second . 

1.2587 

.0011 

Third . 

. 1.2580 

.0011 

Fourth. 

1.2578 

.0011 

Fifth. 

1.2557 

.0011 

Sixth. 

1.2553 

.0011 

Seventh. 

1.2519 

.0006 

Eighth. 

1.2515 

.0006 

Ninth. 

1.2469 

.0006 

Tenth. 

1.2452 

.0006 


is made on the first catch-all, as it is nearest the source of salt. 
If it is very high in salt, the other catch-alls are tested, and if 
they all show high, the operation is stopped, the entire still 
and catch-alls washed out and the distillation started anew. If 
the first catch-all is only slightly over the limit, the distillation 
proceeds, as the other catch-alls will average the salt down. 
Table V shows the results obtained from an actual run of a 
6-foot still fitted with ten catch-alls. 

66. Products of Distillation.—The products of the 
distillation of crude glycerine may be separated into three 
























MANUFACTURE OF SOAP, PART 3 


39 


classes, namely, material collected in the catch-alls, technically 
called distillate; material of a much lighter gravity, called 
sweet water , consisting chiefly of water containing from no 
glycerine at all to as high as 12 per cent.; and a black, viscous 
residuum left in the still, constituting the foots. 

67 . Refined Glycerine. —The contents of the catch-alls 
still contain too much water and are removed to a cylindrical 
tank, called a concentrator , for further refining, which consists 
in the removal of water. The concentrator is provided with 
closed steam coils and a vacuum system. The distillate is 
transferred as quickly as possible from the still to the con¬ 
centrator to save the heat, and the concentration is then 
continued. Practice dictates its length, but 2 to 3 hours is 
usually enough. At the end of the concentration some bone 
black, which acts as a decolorizer, is mixed with some of the 
distillate and drawn into the concentrator. The glycerine is 
then pumped through a small filter press that discharges 
directly into a covered tank. It is drummed at once from this 
tank, allowed to stand overnight to cool, and the drums filled 
up the next day. 

Glycerine in any concentrated form must be handled very 
hot. Added to the slowing up in flowing when cold, is the 
danger of breaking the filter plates when cold glycerine is 
forced through them. 

68. Sweet Water. —The material known as sweet water 
is concentrated to the consistency of crude glycerine and is 
then distilled and the distillate concentrated, as explained for 
refined glycerine. Another use is to take it back into an 
evaporator that is sluggish in its boiling to dissolve the salt 
that collects on the tubes of the steam chest. It saves the 
use of water for this purpose. 

69 . Foots. —There remains to be considered the black 
residuum, or foots, in the crude-glycerine still. All the 
organic matter not removed in the preliminary treatment of 
the lye accumulates in the still and forms this black, viscous 
residue, which, if the distillation is carried too far, becomes 
so hard that it is removed from the still only with great diffi- 


40 


MANUFACTURE OF SOAP, PART 3 


culty. To facilitate its easy handling and the recovery of the 
large quantity of glycerine retained by it, the distillation is 
checked at that stage beyond which there is danger of con¬ 
taminating the distillate with entrained matter from the still. 
The quantity of glycerine present in the foots depends on the 
concentration, and is about 50 per cent. 

In the distillation of crude glycerine, the organic com¬ 
pounds of sodium do not precipitate as do the inorganic com¬ 
pounds, namely, sodium sulphate and sodium chloride, and 
the former, as the mass in the still undergoes concentration, 
remain to constitute the foots. There are present, usually, 
about 5 per cent, of salt, from 20 to 30 per cent, of sodium 
acetate, and from 10 to 15 per cent, of sodium salts of non¬ 
volatile organic acids. 

70. While still soft and comparatively fluid, the foots 
are transferred to a tank and neutralized with sulphuric acid. 
After the gradual addition of the diluted acid and filtering, 
the product is concentrated, forming crude glycerine from 
foots; this is then distilled. About 1,200 pounds of foots 
is obtained from every 10,000 pounds of crude glycerine, 
yielding on distillation about 50 per cent, of glycerine. 

It is the practice in some refineries to shut off the feed supply 
of crude for a few hours near the end of the run and to boil down 
the foots until they show a certain consistency in the sight 
glass, and then run them to the sewer as soon as the steam is 
shut off and the vacuum broken. The price of glycerine of 
course controls this procedure. 

71. The glycerine obtained by the process described con¬ 
stitutes the dynamite glycerine of commerce. It is of a pale 
straw color and requires only subsequent distillation and 
filtration through bone black to become the water-white, 
chemically pure glycerine of the pharmacopoeia. Its specific 
gravity is an important physical characteristic, and is subject 
to considerable variation. A density of 1.263 at 15° C. is 
commonly obtained. 

A sample from each run of refined glycerine is analyzed for 
sodium chloride, ash, carbonaceous residue on ignition, and 


MANUFACTURE OF SOAP, PART 3 


41 


for acidity, both free and combined, in addition to a deter¬ 
mination of the specific gravity. Samples, on standing, tend 
to accumulate color, due doubtless to an oxidation process 
of a nature not clearly understood. 

72. Chemically Pure Glycerine. —To meet the require¬ 
ments of the United States Pharmacopoeia, the dynamite 
grade of glycerine is distilled again and treated with bone 
black and filtered to make it water white. Sometimes the 
same object can be obtained by selecting certain portions of 
the first distillate, treating them with bone black, and 
filtering. This grade of glycerine is only required to be of 
95 per cent, strength and distilled water is added to reduce it. 

73. Saponification Crude Glycerine. —All crude glyc¬ 
erines not made by the method previously described are called 
saponification crudes. These include those recovered from 
the acid saponification and autoclave processes for making 
soap and candles. Sometimes they are called candle crude, or 
Twitchell crude. These crudes are concentrated from lyes 
containing 15 per cent, of glycerol and are easily distinguished 
by their low salt content. They have a specific gravity of 
about 28° Be., and the best grades will contain 90 per cent, of 
glycerol. They are refined exactly as are soap-lye crudes 
and, owing to the absence of salt, are much easier to handle. 

74. The chemical examination of the product, not only 
during the various stages of the refining process, but also at 
its completion, is a matter of the utmost importance. By 
this close watching the refiner is warned of changes too 
delicate for observation, and is thus able to correct in its 
first stages any abnormal behavior that would deteriorate 
the final product. 

The examination of the refined glycerine not only indi¬ 
cates the care exercised in the refining, but forms the basis 
for the valuation and sale. The influence exerted by foreign 
matter in the glycerine on its subsequent use in nitration 
and the manufacture of dynamite demands a searching 
chemical and physical examination that is entirely warranted 
by the danger attending these processes. 


42 


MANUFACTURE OF SOAP, PART 3 


CHEMICAL EXAMINATION OF RAW 
MATERIALS AND PRODUCTS 


INTRODUCTION 

75 . Importance of Chemical Examination. —Every 
large soap manufactory maintains a chemical laboratory and 
employs chemists whose duties are to examine all raw materials, 
thus enabling the purchasing department to avoid losses 
incident to misrepresentation and to insist on a high grade 
of material being offered. The chemist analyzes soap and 
similar products made by competitors, in order to obtain 
the necessary information whereby his employer is enabled 
to duplicate it promptly, if desired, at the same or a lower 
figure. He examines daily the various products that occur 
in routine factory work and promptly informs the superin¬ 
tendent of conditions requiring modification or elimination. 
Glycerine recovery cannot be carried on with complete satis¬ 
faction without some knowledge of the chemical principles 
involved in its formation in soap manufacture and its recovery 
from waste-soap lye. Refined glycerine is sold under a guaran¬ 
tee of its quality, to determine which skill in chemical analysis 
is necessary. As soap manufactories grow in size and as 
competition increases, the services of a chemist become more 
indispensable. It may be truthfully stated that the develop¬ 
ment of the soap industry to its present proportions would not 
have been possible without the aid of the chemist. 

76. In industrial laboratory work, owing to the quickness 
with which the information obtained by chemical analysis is 
desired, many of the analytical methods given in technical 
treatises are seldom or never used, or only in part. In the 
routine laboratory work, absolute accuracy, while desired, is 
not required in every case, it being sufficient that successive 



MANUFACTURE OF SOAP, PART 3 


43 


determinations be performed as accurately as the time will 
permit and that they be uniform, for with uniformity of 
manufacturing operations, the analytical results must be on 
a perfectly comparative basis. 


EXAMINATION OF SOAP STOCK 

77. The following methods of sampling and analysis of 
soap stock have been taken from the report of the committee 
appointed by the American Chemical Society, and, contain all 
the essential features of the methods embodied in the report. 


SAMPLING 

Tank Cars 

1. Sampling While Loading .—Sample shall be taken at 
discharge of pipe where it enters the tank-car dome. The 
total sample taken shall be not less than 50 pounds and shall be 
a composite of small samples of about 1 pound each taken at 
regular intervals during the entire period of loading. The 
sample thus obtained is thoroughly mixed and uniform 
3-pound portions placed in air-tight 3-pound metal containers. 
At least three such samples shall be put up, one for buyer, one 
for seller, and the third to be sent to a referee chemist in 
case of dispute. All samples are to be promptly and correctly 
labeled and sealed. 

2. Sampling From Car On Track. 1 —(a) When contents are 
solid: 2 In this case the sample is taken by means of a large 
tryer measuring about 2 inches across and about 1| times the 
depth of the car in length. Several tryerfuls are taken 
vertically and obliquely toward the ends of the car until 50 
pounds are accumulated, when the sample is softened, mixed, 

1 Live steam must not be turned into tank cars or coils before samples 
are drawn, since there is no certain way of telling when coils are free from 
leaks. 

2 If there is water present under the solid material the fact should be 
noted and the water estimated separately. 

394—12 





44 


MANUFACTURE OF SOAP, PART 3 


and handled as under 1. In case the contents of the tank car 
have assumed a very hard condition, as in winter weather, 
so that it is impossible to insert the tryer and it becomes neces¬ 
sary to soften the contents of the car by means of the closed 
steam coil (in nearly all tank cars the closed steam coil leaks), 
or by means of open steam in order to draw a proper sample, 
suitable arrangements must be made between buyer and seller 
for the sampling of the car after it is sufficiently softened, due 
consideration to be given to the possible presence of water in the 
material in the car as received and also to the possible addition 
of water during the steaming. The committee knows of no 
direct method for sampling a hard-frozen tank car of tallow 
in a satisfactory manner. 

(i b ) When contents are liquid: The sample taken is to 
be. a 50-pound composite made up of numerous small samples 
taken from the top, bottom, and intermediate points by means 
of a bottle or metal container with removable stopper or top. 
This device attached to a suitable pole is lowered to the 
various desired depths, when the top or stopper is removed 
and the container allowed to fill. The 50-pound sample 
thus obtained is handled as under 1. 

(c) When contents are in a semisolid state, or when 
stearine has separated from liquid portions: In this case a 
combination of (a) and (b) may be used by agreement of the 
parties or the whole may be melted and procedure (b) followed. 

Barrels, Tierces, Casks, Drums, and Other Packages 

All packages shall be sampled, unless by special agreement 
the parties arrange to sample a lesser number; but in any case 
not less than 10 per cent, of the total number shall be sampled. 
The total sample taken shall be at least 20 pounds in weight 
for each 100 barrels, or equivalent. 

1. Barrels , Tierces , and Casks. —(a) When contents are solid: 
The small sample shall be taken by a tryer through the bung- 
hole or through a special hole bored in the head or side for the 
purpose, with a 1-inch or larger auger. Care should be taken 
to avoid and eliminate all borings and chips from the sample. 
The tryer is inserted in such a way as to reach the head of the 


MANUFACTURE OF SOAP, PART 3 45 

barrel, tierce, or cask. The large sample is softened, mixed, 
and handled according to Tank Cars 1. 

(b) When contents are liquid: In this case use is made of 
a glass tube with constricted lower end. This is inserted 
slowly and allowed to fill with the liquid, when the upper end 
is closed and the tube withdrawn, the contents being allowed 
to drain into the sample container. After the entire sample is 
taken it is thoroughly mixed and handled according to Tank 
Cars 1. 

(c) . When contents are semisolid: In this case the tryer 
or a‘-glass tube with larger outlet is used, depending on the 
degree of fluidity. 

2. Drums .—Samples are to be taken as under 1, use being 
made of the bunghole. The tryer or tube should be sufficiently 
long to reach the ends of the drum. 

3. Other Packages. —Tubs, pails, and other small packages 
not previously mentioned are to be sampled by tryer or tube 
(depending on fluidity) as already outlined, the tryer or tube 
being inserted diagonally whenever possible. 

4. Mixed Lots and Packages .—When lots of tallow or other 
fats are received in packages of various shapes and sizes, and 
especially wherein the fat itself is of variable composition, 
such must be left to the judgment of the sampler. If variable, 
the contents of each package should be mixed as thoroughly 
as possible and the amount of the individual samples taken 
made proportional to the sizes of the packages. 

5. Color .—It is very important that the color of tallows be 
kept up to certain standards to secure a uniform product. 
An arbitrary color system of standards is made in the labora¬ 
tory by which the melted tallow is compared and given the 
number which it matches the closest. A very good system of 
standards can be made from crude glycerine of graduated 
shades contained in sealed glass tubes. These tubes are of the 
same kind as those in which the sample is melted. They are 
numbered or graded from light to dark. 

78 . Determination of Moisture. — The standard 
method of determining moisture employs a vacuum oven, 


46 


MANUFACTURE OF SOAP, PART 3 


but as only large laboratories are so equipped, a method com¬ 
paring favorably in results is given. 

Method .—Weigh out about 5 grams of the prepared sample 
into a tared dish. Dry to constant weight in a well-ventilated 
oven held at a uniform temperature between 105° and 110° C. 
The thermometer bulb should be close to the dish. Constant 
weight is attained when successive dryings for 1-hour periods 
show a loss of not over .05 per cent. The loss should be 
reported as moisture and volatile matter. 

The standard dish is made of glass, shallow, lipped, and 
beaker form, approximately 6 to 7 centimeters in diameter and 
4 centimeters deep. 

The air-drying oven is not even approximately accurate 
for drying and semidrying oils and those of the coconut-oil 
group. These oils should be tested only in a vacuum oven, for 
which the method is the same. 

A quick qualitative test for much moisture can be made by 
dropping some of the tallow or oil into the heated bowl of a 
metal spoon. If a cracking noise or frothing takes place, 
moisture is present. It is necessary to keep the spoon 
hot. 


79. Determination of Free Fatty Acids. —The deter¬ 
mination of free fatty acids is one of the most important 
tests applied to soap stock, as it gives not only an indication 
of the value of the stock as a source of glycerine, but of the 
care exercised in its manufacture and of its origin. The per¬ 
centage of free fatty acids in soap stock varies, being greater 
in the summer than in the winter, owing to the fact that the 
agents of decomposition are more active in the former season. 
This is shown in Table VI. 

As about 10 per cent, of glycerol is theoretically available 
from soap stocks, a free fatty acidity of 10 per cent, will 
indicate a loss of 1 per cent, of glycerol, calculated on the 
basis of the stock, or 10 per cent., calculated on the amount 
of glycerol theoretically available. 

The method of procedure is as follows: Heat the sample 
sufficiently to melt it, and transfer 5 cubic centimeters to an 


MANUFACTURE OF SOAP, PART 3 


47 


Erlenmeyer flask having a wide mouth and a capacity of 
250 cubic centimeters; weigh, and add about 50 cubic centi¬ 
meters of hot, neutral, 95-per-cent, alcohol. Shake well for a 
few minutes, then add a few drops of alcoholic phenol- 
phthalein solution and titrate with half-normal sodium- 
hydroxide solution until a permanent pink color is obtained. 


TABLE VI 

PERCENTAGES OF FREE FATTY ACIDS 


Months 

Lots 

Free Fatty Acid 
Per Cent. 

January . 

58 

4.31 

February. 

55 

4.09 

March . 

61 

4.27 

April. 

63 

5.28 

May. 

47 

5.36 

June. 

63 

6.39 

July . 

53 

8.03 

August. 

81 

8.19 

September. 

68 

7.28 

October . 

63 

7.01 

November . 

54 

5.12 

December . 

75 

4.58 


Calculate free fatty acids in terms of oleic acid the molecular 

N 

weight of which is 282. One cubic centimeter of — NaOH 

= .141 gram of oleic acid. Assuming that x cubic centimeters 
N 

of — NaOH is required for neutralization, the percentage of 
A 

free fatty acids may be found according to the following 
formula: 


Percentage of 1 
free fatty acids J 


N 

X C. C. — 


NaOHX.UIXlOO 


weight taken 

























48 


MANUFACTURE OF SOAP, PART 3 


The free-fattty-acid determination, with alcohol as a sol¬ 
vent, is based on the practical insolubility of neutral glyc¬ 
erides in alcohol, while the free fatty acids are soluble. 

By measuring a definite volume of the liquid fat, much 
time is saved, it being a simple matter to ascertain the average 
weight of 5 cubic centimeters of the soap stock usually examined. 

It is customary to calculate free fatty acid to oleic acid 
except in the cases of palm oil, coconut oil, and palm-kernel 
oil. The fatty-acid content of palm oil is expressed in terms 
of palmitic acid while that of coconut and palm-kernel oils is 
expressed as lauric acid. The molecular weights of palmitic 
and lauric acids are respectively 256 and 200. They are 
both monobasic acids. 

In order to obtain the best results in making a determination 
of free fatty acids, 95 per cent, ethyl alcohol, freshly distilled 
over solid caustic soda, or caustic potash, should be used. 
However, methyl alcohol and ethyl alcohol denatured with 
methyl alcohol may be substituted in routine work but they 
do not give as sharp end points as does ethyl alcohol. 

80. Titer Test.—Soap stock of animal origin is bought 
and sold on the titer, by which is meant the highest temperature 
produced by the latent heat of fusion that is liberated on the 
solidification of the pure liquid fatty acids obtained from the 
stock. 

To obtain reliable results by whichever modification of 
the method is used, it is essential that each determination be 
made under precisely uniform conditions and from fatty acids 
prepared in the same mnner. This determination may also 
be applied to cottonseed and coconut oils. For the former 
stock, it is a reliable index of the soap-making qualities of 
different samples of oil. 

Since all tallows and greases are bought on this test, and 
since it is by far the most important test that can be given to 
a stock, it should in all cases be performed where a chemist is 
employed. 

Standard Thermometer .—The thermometer is graduated at 
zero and in tenths of degrees from 10° C. to 65° C. with one 


MANUFACTURE OF SOAP, PART 3 


49 


auxiliary reservoir at the upper end and another between the 
zero mark and the 10° mark. The cavity in the capillary tube 
between the zero mark and the 10° mark is at least 1 centi¬ 
meter below the 10° mark, and the 10° mark is about 3 or 4 
centimeters above the bulb. The length of the thermometer is 
about 37 centimeters over all. The thermometer has been 
annealed for 75 hours at 450° C. and the bulb is of Jena normal 
glass, or its equivalent, moderately thin, so that the ther¬ 
mometer will be quick-acting. The bulb is about 3 centi¬ 
meters long and 6 millimeters in diameter. The stem of the 
thermometer is 6 millimeters in diameter and made of the 
best thermometer tubing, with scale etched on the stem. 
The graduations are clear-cut and distinct, but quite fine. 
The thermometer must be certified by the U. S. Bureau of 
Standards. 

Glycerine-Caustic Solution .—Dissolve with the aid of heat 
250 grams potassium hydroxide in 1,000 cubic centimeters 
of dynamite glycerine. 

Determination .—Heat 75 cubic centimeters of the glycerine- 
caustic solution to 150° C. and add 50 grams of the melted fat. 
Stir the mixture well and continue heating until the melt is 
homogeneous, at no time allowing the temperature to exceed 
150° C. Allow to cool somewhat and carefully add 50 cubic 
centimeters of 30-per-cent, sulphuric acid. Now add hot 
water and heat until the fatty acids separate out perfectly 
clear. Draw off the acid water and wash the fatty acids with 
hot water until free from mineral acid, then filter and heat to 
130° C. as rapidly as possible with stirring. Transfer the 
fatty acids, when cooled somewhat, to a l"X^" titer 
tube, placed in a 16-ounce, wide-mouth bottle of clear glass, 
fitted with a cork that is perforated so as to hold the tube 
rigidly when in position. Suspend the titer thermometer 
so that it can be used as a stirrer and stir the fatty acids 
slowly (about 100 revolutions per minute) until the mercury 
remains stationary for 30 seconds. Allow the thermometer to 
hang quietly with the bulb in the center of the tube and report 
as the titer of the fatty acids the highest point to which the 
mercury rises. The titer should be made at about 20° C. 


50 


MANUFACTURE OF SOAP, PART 3 


for all fats having a titer above 30° C. and at 10° C. below the 
titer for all other fats. 

For American tallows the titer should fall between 41° and 
44° C.; for cottonseed oil, between 32° and 33° C.; and for 
coconut oil, between 23° and 25° C. Cochin oil is usually close 
to 25° C. The higher the titer the more desirable the material 
is as a soap stock. 

81. Special Tests.—For the proper identification and 
test for purity of fats and oils, there are numerous tests that 
can be employed. All the fats and oils have some chemical and 
physical properties that are constant between certain limits. 
The variations are due to locality of origin, method of extrac¬ 
tion, refining, etc. Among these constants are the iodine 
value and the saponification value. 

82. Iodine Value. —Fats and saponifiable oils have the 
property of absorbing iodine chloride because of the unsatu¬ 
rated fatty acids and glycerides which they contain. The 
percentage of iodine chloride which it absorbs, expressed in 
terms of iodine, is called the iodine value of the compound. 


WIJS METHOD FOR DETERMINATION OF IODINE VALUE 

83. Preparation of Reagents. —Wijs Iodine Solu¬ 
tion .— (1) Dissolve separately 7.9 grams of iodine trichloride 
and 8.7 grams of iodine in glacial acetic acid on the water bath, 
taking care that the solutions do not absorb moisture. The two 
solutions are then poured into a 1,000 cubic centimeter flask, 
which is then filled up to the mark with glacial acetic acid. 

Or (2) dissolve 6.5 grams of resublimed iodine in 1 liter of 
C. P. glacial acetic acid and pass in washed and dried chlorine 
gas until the original sodium-thiosulphate titration of the 
solution is just doubled. This solution is then preserved in 
amber glass-stoppered bottles, sealed with paraffin until 
ready for use. 

jq Sodium-Thiosulphate Solution .—Dissolve 24.8 grams of 

C. P. sodium thiosulphate and dilute with water to 1 liter at 
the temperature at which the titrations are to be made. 



MANUFACTURE OF SOAP, PART 3 


51 


Starch Paste. Boil 1 gram of starch in 200 cubic centimeters 
of distilled water for 10 minutes and cool to room tempera¬ 
ture. 

Potassium-Iodide Solution. —Dissolve 150 grams of potassium 
iodide in water and make up to 1 liter. 

N 

1 q P°tassium-Bichromate Solution. —Dissolve 4.903 grams of 

C. P. potassium bichromate in water and make the volume 
up to 1 liter at the temperature at which titrations are to be 
made. One cubic centimeter = .012685 gram iodine. 

Standardization of Sodium-Thiosulphate Solution. —Place 20 
cubic centimeters of the potassium-bichromate solution, to 
which has been added 10 cubic centimeters of the solution of 
potassium iodide, in a glass-stoppered flask. Add to this 
5 cubic centimeters of strong hydrochloric acid. Dilute with 

N 

100 cubic centimeters of water, and allow the Jq sodium 

thiosulphate to flow slowly into the flask until the yellow color 
of the liquid has almost disappeared. Add a few drops of the 
starch paste, and with constant shaking continue to add the 
N 

Jq sodium-thiosulphate solution until the blue color just 
disappears. 

Determination. —Weigh accurately from .10 to .50 gram, 
depending on the iodine number, of the melted and filtered 
sample into a clean, dry, 16-ounce glass-stoppered bottle 
containing 15 to 20 cubic centimeters of carbon tetrachloride 
or chloroform. Add 25 cubic centimeters of iodine solution 
from a pipette, allowing the latter to drain for a definite time. 
The excess of iodine should be from 50 to 60 per cent, of the 
amount added, that is, from 100 per cent, to 150 per cent, of 
the amount absorbed. Moisten the stopper with a 10-per-cent, 
potassium-iodide solution to prevent loss of iodine or chlorine, 
but guard against an amount sufficient to run down inside the 
bottle. Let the bottle stand in a dark place for J hour at a 
uniform temperature. At the end of that time add 20 cubic 
centimeters of 10-per-cent, potassium-iodide solution and 
100 cubic centimeters of distilled water. Titrate the iodine 


52 


MANUFACTURE OF SOAP, PART 3 


N 

with Jq sodium-thiosulphate 


solution, which 


is added 


gradually with constant shaking, until the yellow color of the 
solution has almost disappeared. Add a few drops of starch 
paste and continue titration until the blue color has entirely 
disappeared. Toward the end of the reaction, stopper the 
bottle and shake violently so that any iodine remaining in 
solution in the tetrachloride or chloroform may be taken up 
by the potassium-iodide solution. Conduct two determina¬ 
tions on blanks, which must be run in the same manner as 
the sample except that no fat is used in the blanks. Slight 
variations in temperature quite appreciably affect the volume 
of the iodine solution, as acetic acid has a high coefficient of 
expansion. It is, therefore, essential that the blanks and 
determinations on the sample be made at the same time. 
The number of cubic centimeters of standard thiosulphate 
solution required by the blank, less the amount used in the 
determination, gives the thiosulphate equivalent of the iodine 
absorbed by the amount of sample used in the determination. 
Calculate to centigrams of iodine absorbed by 1 gram of sample. 

To illustrate the application of the Wijs method, assume 
that, in making a determination, .1355 gram of linseed oil 
was weighed and treated with 25 cubic centimeters of the 
iodine solution. In a blank test 61.2 cubic centimeters of 
sodium-thiosulphate solution were needed for the iodine solu¬ 
tion. In the determination 41.1 cubic centimeters of sodium- 
thiosulphate solution were required to titrate the excess of 
iodine. Therefore the iodine absorbed by the oil was equiva¬ 
lent to 20.1 cubic centimeters of sodium-thiosulphate solu¬ 
tion : 20 cubic centimeters of the bichromate solution = .2537 

gram iodine. It required 20.8 cubic centimeters of the sodium- 
thiosulphate solution in the standardization to titrate the 
20 cubic centimeters of bichromate solution. Therefore, 
20.8 cubic centimeters of sodium thiosulphate = .2537 gram 

iodine and, 

20.1 cubic centimeters of sodium thiosulphate = .24516 gram 

iodine. 


.24516X100 


= 181, the iodine value of the linseed oil used. 


.1355 



MANUFACTURE OF SOAP, PART 3 


53 


84. Saponification Number. —The number of milli¬ 
grams of potassium hydroxide required for the complete 
saponification of 1 gram of fat or oil is called the saponifica¬ 
tion number , or Koettstorfer number. The reagents required are 
N 

2 hydrochloric acid, carefully standardized, and a solution 


of alcoholic potassium hydroxide, prepared as follows: Dis¬ 
solve 40 grams of pure potassium hydroxide in 1 liter of 95- 
per-cent. redistilled alcohol. The alcohol should be redistilled 
from potassium hydroxide over which it has been standing for 
some time, or with which it has been boiled for some time, 
using a reflux condenser. The solution must be clear and 
the potassium hydroxide free from carbonate. 

Determination. —Weigh accurately about 5 grams of the 
filtered sample into a 250 to 300 cubic centimeter Erlenmeyer 
flask. Pipette 50 cubic centimeters of the alcoholic potassium- 
hydroxide solution into the flask, allowing the pipette to 
drain for a definite time. Connect the flask with an air 
condenser and boil until the fat is completely saponified (about 

N 

30 minutes). Cool and titrate with the — hydrochloric acid, 

using phenolphthalein as an indicator. Calculate the Koett¬ 
storfer number (mg. of potassium hydroxide required to 
saponify 1 gram of fat). Conduct two or three blank deter¬ 
minations, using the same pipette and draining for the same 
length of time as above. 

To illustrate the application of the method, assume that, 
in making a determination, 1.4812 grams of olive oil was 
weighed out and saponified with 25 cubic centimeters of 
alcoholic-potash solution, and that 15.2 cubic centimeters 


N 

2 


HCl was required 


to 


titrate back the excess of alkali. 


N 

blank required 25.4 cubic centimeters — HCl) therefore, 


The 

10.2 


cubic centimeters represents the alkali absorbed. 
Calculation of Results .— 

10.2X.02805 = .28611 g. KOH = 286.11 mg. KOH 
286.11-^1.4812 = 193.2, saponification number 


54 


MANUFACTURE OF SOAP, PART 3 


Table VII gives the iodine and saponification values of 
some of the more common oils. 


TABLE VII 

IODINE AND SAPONIFICATION VALUES OF COMMON OILS 


Name of Oil 

Iodine 

Value 

Saponification 

Value 

Castor . 

87 to 93 

183 to 186 

Coconut . 

8.4 to 9.3 

246 to 260 

Corn. 

119 to 122 

188 to 193 

Cottonseed . 

111 to 115 

193 to 195 

Linseed. 

179 to 209 

192 to 195 

Olive. 

86 to 90 

185 to 196 

Palm. 

51 to 53 

196 to 205 

Palm-kernel. 

13 to 17 

242 to 250 

Peanut . 

96 to 103 

190 to 196 

Rape. 

99 to 103 

170 to 179 

Soya-bean. 

138 to 142 

195 

Tung . 

144 to 159 

193 

Tallow, beef . 

40.5 to 42 

193 to 200 

Tallow, mutton . 

34 to 35 

192 to 195 



ANALYSIS OF ROSIN 

85 . Determination of Unsaponifiable Matter.—The 
only chemical test commonly applied to rosin is the determi¬ 
nation of the unsaponifiable matter, which increases, as 
previously stated, as the quality of the rosin decreases. 
The grading accorded the barrel from which the sample is 
taken is determined by comparing with standard cubes a cube 
cut from the sample, with dimensions equal to those of the 
standard. Care should be taken to have the sample cube 
representative of the quality of rosin in the barrel. The 
unsaponifiable matter present is determined in the same 
manner as the unsaponifiable matter in glyceride stock. 

86. Comparison With Standards. —Rosin of a given 
grade should correspond in color and clearness with the 

























MANUFACTURE OF SOAP, PART 3 


55 


standard cube of the same grade. The standards should be 
renewed from time to time, as they tend to bleach on exposure 
and to lose the cube shape through softening. In comparing 
samples with the standards, strict uniformity of dimensions 
and exposure to light must be observed. 


ANALYSIS OF SODA ASH 

87. Determination of Sodium Carbonate. —In order 
to determine the amount of sodium carbonate present in soda 
ash, weigh 1 or 2 grams of the sample into a 500-cubic-centi- 
meter flask and dissolve in water; add a few drops of phenol- 
phthalein as indicator. Run in from a burette an accurately 
measured excess of half-normal sulphuric acid and boil to 
expel all traces of carbon dioxide. Titrate the excess of acid 
with half-normal caustic soda. The solutions are equal and 
are known in terms of the various sodium compounds. The 
weight of sodium carbonate corresponding to the number of 
cubic centimeters of half-normal sulphuric acid required to 
neutralize the soda ash multiplied by 100 is divided by 
the weight of alkali taken, and the result is the percentage 
of actual anhydrous sodium carbonate present in the soda ash. 

88. Determination of Total Alkali. —To determine 
the total alkali present, dissolve 10 grams of the soda ash in 
about 150 cubic centimeters of warm distilled water and dilute 
to 1 liter. Remove 50 cubic centimeters of this solution to a 
beaker and titrate with half-normal sulphuric acid, using 
methyl orange as indicator. Since 1 cubic centimeter of 
half-normal acid is equivalent to .03082 gram of Na 2 0, the 
percentage of Na 2 0 in the soda ash will be found by multi¬ 
plying the number of cubic centimeters of half-normal acid 
required by .03082X20X100 and dividing the result by 10 
(the weight of the sample taken). 



56 


MANUFACTURE OF SOAP, PART 3 


ANALYSIS OF COMMERCIAL CAUSTIC SODA 

89. Determination of Total Alkali. —The determina¬ 
tion of the total amount of alkali present in commercial 
caustic soda is carried out exactly as explained for the deter¬ 
mination of the total alkali of soda ash. The percentage of 
total alkali is expressed in terms of sodium oxide. 

90. Determination of Sodium Hydroxide. —To deter¬ 
mine the actual amount of sodium hydroxide in commercial 
caustic soda, weigh out about 5 grams of the sample from a 
glass-stoppered weighing bottle and as quickly as possible 
add distilled water that has previously been boiled and cooled. 
Transfer to a 250-cubic-centimeter graduated flask, make up 
to the mark and mix thoroughly. Take out 25 cubic centi¬ 
meters and dilute with 50 cubic centimeters of the same dis¬ 
tilled water. Add 3 or 4 drops of phenolphthalein solution 

N 

and titrate slowly with — hydrochloric acid, stirring vigorously 

o 

until only a faint pink remains, and note the reading. Then 
add 1 or 2 drops of methyl-orange solution and resume the 
titration with the same acid until only a faint pink remains. 

Twice the amount of acid used in the methyl-orange titra¬ 
tion equals the amount of sodium carbonate present. The 
result obtained when this amount is subtracted from the total 
acid used indicates the amount of sodium hydroxide present. 

N 

1 c.c. — HCl = .01061 g. Na^COz 
N 

1 c.c. - HCl = .008012 g. NaOH 

Calculate the amount of each present in 250 cubic centi¬ 
meters. 

The theory on which the method is based is, that in mixtures 
of caustic and carbonate-of-soda solutions, the entire caustic 
and only one-half the carbonate are neutralized in the presence 
of phenolphthalein as an indicator, when the acid is added 
slowly to the cold solution and the latter well stirred. This is 
due to the formation of sodium bicarbonate ( NaHCOz ), which 


MANUFACTURE OF SOAP, PART 3 


57 


does not react with phenolphthalein but gives a complete 
end point with methyl orange. Therefore, the safe use of 
the method depends on losing none of the carbonic acid. 


91. Determination of Sodium Chloride. —The lower 
grades of caustic soda contain salt. To determine the salt, 
take 25 cubic centimeters of the sample solution, add a drop 
of methyl orange, and make slightly acid with nitric acid. Add 
a slight excess of pure calcium carbonate, stir well and filter. 
Wash with hot water, add a few drops of a 5-per-cent, potas¬ 
sium-chromate solution and titrate to a slight red color with 
N . 

~ silver-nitrate solution. 

10 N 

1 c. c. — silver-nitrate solution = .005846 g. sodium chloride. 


To illustrate the method of using the results obtained by 
carrying out the methods of analysis for sodium hydroxide, 
sodium carbonate, and sodium chloride, assume that 58.4 c. c. ot 
N 

— HCl were required for the phenolphthalein titration, .66 c. c. 

5 N 

for the methyl-orange titration, and 3.7 c. c. of the — silver- 

nitrate solution for the sodium-chloride determination. 

N 

Then, 58.4 c. c. — HCl for phenolphthalein 

o 

N 

.6 c. c. — HCl for methyl orange 
5 


59.0 

1.2 


57.8 c. c. = sodium hydroxide 
1.2 c. c. = sodium carbonater 
N 

— HCl = . 008012 g. sodium hydroxide 
5 

N 

1 c. c — HCl = . 01061 g. sodium carbonate 
5 


1 c. c. 


57.8X.008012X100 
.5 (wt. of sample) 
1.2 X.01061X100 
.5 (wt. of sample) 


92.62 per cent. 


= 2.55 per cent. 







58 • MANUFACTURE OF SOAP, PART 3 

N 

1 c. c. — AgNC >3 = .005846 g. of sodium chloride 

3.7X.005846X100 , _ 

-=4.32 per cent. 

.5 (wt. of sample) 

From the foregoing results, the analysis would be reported 
as: 


Per Cent. 


Sodium hydroxide .92.62 

Sodium carbonate . 2.55 

Sodium chloride. 4.32 


99.49 


This expressed in percentage of Na 2 0 and as degrees would 
make it of the 74° grade. 


92. Caustic potash and pearl ash are examined in the 
same manner. If the quantity of potash purchased war¬ 
rants the work, the percentage of caustic soda, sodium car¬ 
bonate, potassium chlorides, and the alkali sulphates may be 
determined. These compounds are present as impurities. 


ROUTINE CHEMICAL EXAMINATION OF KETTLE- 

ROOM PRODUCTS 


ANALYSIS OP WASTE SOAP LYE 

93. Determination of Total Alkali. —In order to 

determine the total alkali present in the waste soap lye, trans¬ 
fer 10 cubic centimeters of waste lye into a clean, 500-cubic- 
centimeter flask by means of a pipette. Dilute with 150 
cubic centimeters of water, add phenolphthalein as indicator, 
and run in from a burette sufficient half-normal sulphuric 
acid to discharge the pink color. Boil to expel carbon 

dioxide and titrate back with seminormal caustic soda. 

N 

Illustration. —Long Method .—The amount of ~ HiSO\ required for 

N 

neutralization is 1.94 cubic centimeters; 1 cubic centimeter of “ H^SOi 

equals .02 gram of NaOH. Total alkali, estimated as NaOH , equals 
1.94 X.02X100 

= .388 gram of NaOH in 100 cubic centimeters of liquor. 


10 










MANUFACTURE OF SOAP, PART 3 


59 


Cubic 


Short Method. — Centimeters 

N 

Total amount of — H 2 S0 4 used is.5.90 


N N 

Amount of ^ NaOH used for titrating excess of ~ H 2 S0 4 is 3.96 

N 

Amount of ~ H 2 S0 4 absorbed. 1.94 


The total alkali, estimated as NaOH , is 1.94X.2 = .388 gram of NaOH 
in 100 cubic centimeters of liquor. 

It will be observed that these methods give the percentage of alkali 
by volume; the percentage by weight would be slightly less. 


94. Determination of Sodium Chloride. —In order 
to determine the sodium chloride contained in the waste 
soap lye, transfer 5 cubic centimeters of waste lye into a 
100-cubic-centimeter beaker by means of a pipette and dilute 
with 50 cubic centimeters of distilled water. Mix well and 
transfer 5 cubic centimeters of the diluted lye to a 4-inch 
porcelain evaporating dish. Now add dilute nitric acid to a 
slight excess, then pure calcium carbonate. Stir the contents 
of the dish, filter, wash with hot water and titrate the filtrate 
with decinormal silver-nitrate solution, using postassium 
chromate as indicator. Calculate the percentage of sodium 
chloride as if 5 grams of lye had been taken for analysis. 


Illustration. —Amount of waste lye taken is 5 cubic centimeters; 
N 

amount of — AgNOz required is 20.5 cubic centimeters. 


20.5 X.005846X100 


= 2.35 per cent, of NaCl (by volume) 


The true percentage by weight is found by dividing the preceding 
result by the specific gravity of the waste lye. 

95. Determination of Glycerol.— As the glycerol 
determination requires some time, it is only done when special 
information as to the glycerol content of a particular lye is 
desired, or when crude glycerine is being purchased, on 
glycerol content, for refining. The analytical methods used 
industrially are based on the complete oxidation of glycerol 
to carbon dioxide and water. Potassium bichromate and sul¬ 
phuric acid are used to effect the oxidation. In another, the 

394—13 







60 


MANUFACTURE OF SOAP, PART 3 


acetin process, the quantitative determination of the glycerol 
is based on its transformation into glyceryl triacetin, in accor¬ 
dance with the following equation: 

2C i H 6 (0&)i+S(CH s -C0)2-0 = 2C t H 6 (CHiC00)s+3Hi0 

This method, when carried out by a chemist who is skilled 
in its operation, gives the most accurate results. One great 
source of error in all the oxidation methods for the determina¬ 
tion of glycerol is the danger of oxidizing organic impurities 
that are incompletely removed from the solution. As a result, 
all oxidation methods give uniformly high results. In the 
acetin method, only the glyceride is susceptible to the action 
of the acetic anhydride. 

96. Acetin Method. —When the acetin method is 
employed, about 1| grams of crude glycerine is heated with 
7 or 8 grams of acetic anhydride and 3 grams of anhydrous 
sodium acetate. The function of the last reagent is to absorb 
water. The mixture is gently boiled for 1J hours in a flask 
provided with a water-cooled, reflux condenser. At the 
expiration of this period, cool the contents of the flask and 
introduce 50 cubic centimeters of water through the condenser. 
With the condenser attached, agitate with slight warming 
until the oily matter in the bottom of the flask has dissolved. 
Filter when cool, and to the filtrate add a few drops of phenol- 
phthalein. Run in dilute caustic soda (20:1,000) from a 
burette until just neutral (until the yellow color just changes 
to reddish yellow). The free acid is thus neutralized. Now 
run in from a burette a measured quantity, usually about 25 
cubic centimeters, of caustic-soda solution of known strength 
(about twice normal or a little stronger). Heat the contents 
of flask on a water bath and titrate the excess of caustic soda 
with normal hydrochloric acid. The percentage of glycerol 
present, as calculated from the amount of sodium hydroxide 
used to saponify the triacetin, will be evident from the follow¬ 
ing calculation: 

Illustration.—T he amount of sodium-hydroxide solution added 
after neutralization was 27.15 cubic centimeters. Assume that one cubic 
centimeter of the sodium-hydroxide solution used equals 2.42 cubic centi- 


MANUFACTURE OF SOAP, PART 3 


61 


meters of normal hydrochloric acid. Therefore, 27.15 cubic centimeters 
X2.42 = 65.70 cubic centimeters, the equivalent of 27.15 cubic centimeters 
of sodium hydroxide in normal hydrochloric acid. 

After saponification, 33.2 cubic centimeters of normal hydrochloric 
acid was required to neutralize the excess of sodium hydroxide; 65.7 cubic 
centimeters less 33.2 cubic centimeters equals 32.5 cubic centimeters 
of normal hydrochloric acid, which is equivalent to the sodium hydroxide 
required for the saponification of the triacetin. One cubic centimeter of 
normal acid equals .03069 gram of glycerol, 32.5 cubic centimeters of 
normal acid equals .99742 gram of glycerol; weight taken for analysis 
equals 1.2501 grams. 

.99742X100 

—— =79.78 per cent, glycerol present 

97. Bichromate Oxidation Method. —The bichromate 
oxidation method is based on the fact that 1 gram of glycerol is 
completely oxidized to carbon dioxide by 7.4564 grams of 
potassium bichromate in the presence of sulphuric acid. It 
does not require the skill of manipulation of the acetin method, 
but unfortunately it does not give as accurate results because 
of the oxidation of organic matter, other than glycerol, which 
may also be present. The following reagents are required: 

Potassium bichromate. —The very purest salt obtainable is 
powdered and dried at 140° C. and kept in a tight-fitting 
glass-stoppered bottle. 

Mohr's salt. — FeS0^{NH\) 2 S0^6H 2 0. — Dissolve 3.7282 
grams of the dry K 2 Cr 2 0 7 in 30 c. c. of water, add 50 cubic 
centimeters of 50 per cent. H 2 SO\ and to the cold undiluted 
solution add a moderate excess of Mohr’s salt from a tared 
weighing bottle. Titrate back the excess of Mohr’s salt with 
the K 2 Cr 2 0 7 solution described later. Calculate the value of 
the Mohr’s salt in terms of K 2 Cr 2 0 7 . 

Standard K 2 Cr 2 0 7 Solution. —Dissolve 7.4564 grams K 2 Cr 2 0 7 
in 1,000 cubic centimeters water. 1 cubic centimeter contains 
.0074564 gram I< 2 Cr 2 0 7 = .001 gram glycerol. 

Basic Lead Acetate. —Dissolve 235 grams of lead acetate in 
1,000 cubic centimeters of water; boil, and stir in 165 grams of 
litharge. Boil and stir 15 minutes. 

Silver Acetate. —A saturated solution is prepared at ordinary 
temperatures (about 20° C.). 



62 


MANUFACTURE OF SOAP.. PART 3 


Dilute Sulphuric Acid. —Add 150 cubic centimeters H 2 SO± 
to 850 cubic centimeters of water, with the usual precautions. 

The method of procedure is to weigh out 20 grams of the 
crude glycerine, make up to 250 cubic centimeters, and mix 
thoroughly. Pipette off 25 cubic centimeters into a 50- 
cubic-centimeter beaker and add a slight excess of the basic 
acetate-of-lead solution. Wash several times by decantation, 
decanting through a filter into a 250-cubic-centimeter gradu¬ 
ated flask. Pour precipitate on the filter and wash thoroughly. 
Add 12 cubic centimeters saturated silver-acetate solution 
and a slight excess of dilute sulphuric acid (about 5 cubic 
centimeters) and make it up to the mark with .2 cubic centi¬ 
meter excess to allow for volume of precipitate. Mix well. 
Filter through a dry filter and reject first portion, collecting 
the balance in a glass-stoppered 250-cubic-centimeter flask. 

Weigh out 1.8641 grams of the K 2 Cr 2 0 7 into a 150-cubic-centi¬ 
meter beaker (previously cleaned with K 2 Cr 2 0 7 and H 2 SOa 
solution and washed with distilled water). Add 25 cubic 
centimeters distilled water and then 25 cubic centimeters of 
the clear filtrate to be tested and stir until the K 2 Cr 2 0 7 is 
dissolved. Add with constant stirring 25 cubic centimeters 
of concentrated H 2 SO±, transfer to a steam bath and oxidize for 
30minutes, keeping the beaker covered with an absolutely clean 
watch glass. Remove from the bath and add a slight excess 
of Mohr’s salt from a tared weighing bottle and titrate back 
the excess with the standard K 2 Cr 2 0 7 solution, using potassium 
ferricyanide on a white spot plate as an indicator. 

Calculation of Results. —Because of the manner in which the 
20-gram sample of crude glycerine • was diluted, namely, the 
20 grams to 250 cubic centimeters and 25 cubic centimeters of 
this solution to 250 cubic centimeters, the 25-cubic-centi¬ 
meter portion of the latter solution, that was treated with 
potassium bichromate, contains only .2 gram of crude glycer¬ 
ine, or T -Jo of the original sample. Assume that in this par¬ 
ticular analysis, 1.8641 grams of solid I\ 2 Cr 2 0 7 are added to .2 
gram of the crude glycerine, in order to oxidize the glycerol 
that it contains. This quantity of K 2 Cr 2 0 7 is more than 
enough to oxidize the glycerol in the .2-gram sample, since 



MANUFACTURE OF SOAP, PART 3 


63 


7.45G4 grams K 2 Cr 2 0 7 will oxidize 1 gram of glycerol. There¬ 
fore K 2 Cr 2 0 7 will be present in excess and the exact excess is 
determined by means of Mohr’s salt and the standard K 2 Cr 2 0 7 
solution. Assume that of the particular Mohr’s salt used, 
8.015 grams were equivalent to 1 gram of K 2 Cr 2 0 7 , that 5.4892 
grams of Mohr’s salt were added to reduce the excess K 2 Cr 2 0 7 , 
and that 7.3 cubic centimeters of the standard K 2 Cr 2 0 7 solu¬ 
tion were required to oxidize the excess of Mohr’s salt added. 

1 c. c. K 2 Cr 2 0 7 solution = .0074564 g. K 2 Cr 2 0 7 
7.3 c. c. K 2 Cr 2 0 7 solution = .0544 g. K 2 Cr 2 0 7 

1 g. A 2 6V 2 0 7 = 8.015 g. Mohr’s salt 
.0544 g. A 2 CY 2 0 7 = .436 g. Mohr’s salt 
The excess of Mohr’s salt used is then .436 gram. The total 
quantity of Mohr’s salt used was 5.4892 grams. Then, 

5.4892 — .436 = 5.0532 grams 

of Mohr’s salt actually used up in reducing the excess K 2 Cr 2 0 7 . 

1 g. Mohr’s salt = .124 g. K 2 Cr 2 0 7 
5.0532 g. Mohr’s salt = .6265 g. K 2 Cr 2 0 7 , which represents 
the excess. Then, 

1.8641 —.6265 = 1.2376 g. K 2 Cr 2 0 7 actually required to 
oxidize the glycerol in the .2-gram sample. 

1 g. K 2 Cr 2 0 7 =. 134 g. glycerol 

1.2376 X .134 = .1658 g. glycerol in the sample 


.1658X100 

.2 


= 82.9 per cent, glycerol in the sample 


This is a modification of the general method, but has a great 
advantage in using the dry salts in place of the concentrated 
solutions. It gives excellent results. 

Glycerol in Filter-Press Cake. —Extract 10 grams of the cake 
five or six times with boiled, distilled water, using about 350 
cubic centimeters in all. Evaporate the filtrate to 75 cubic 
centimeters; purify with lead acetate, silver acetate, and sul¬ 
phuric acid by the method just given. The solution is made 
up to exactly 250 cubic centimeters and one-fifth or one-tenth 
taken for oxidation. The rest of the analysis is carried out as 
directed in the method already given. 

Glycerol in Recovered Salt. —Extract a 10-gram sample of the 
salt with an alcohol-ether (1:3) solution. Evaporate the 



64 


MANUFACTURE OF SOAP, PART 3 


extract to expel the alcohol and ether. This is done on a 
steam bath and may be hastened by adding small amounts of 
water after the extract has been concentrated to a small vol¬ 
ume. The alcohol will evaporate quicker if this is done and 
there is less danger of losing glycerine. When the alcohol has 
been removed, the extract is diluted, purified, and oxidized 
by the method given. 


SOAP ANALYSIS AND THE INTERPRETATION 

OF RESULTS 


98. Assume that a cake of soap made by the boiled 
settled process analyzed as follows: 


Per Cent. 


Water.31.27 

Fatty anhydride.37.57 

Rosin anhydride.20.28 

Combined alkali. 6.57 

Free caustic alkali .none 

Free carbonated alkali. 2.51 

Salt.21 

Unsaponifiable . 1.08 

Undetermined.51 


100.00 


or 


Then combining the ingredients according to their existing 
state in the soap, the analysis would appear as follows: 

Per Cent. 


Water. 

Combined alkali as Na 2 0 

Soap < Fatty anhydrides. 

Rosin anhydrides . 

Carbonated alkali, Na 2 C0 3 
Salt. 


Unsaponifiable . 

Undetermined (glycerol, etc.) 


6.57 
37.57 >. 
20.28 


31.27 

64.42 

2.51 

.21 

1.08 

.51 


100.00 


99. It will be assumed that the sample analyzed is a 
fairly fresh piece of soap, not having undergone much dry- 























MANUFACTURE OF SOAP, PART 3 


65 


ing. Settled rosin soap fresh from the cutting table is known 
to contain from 30 to 35 per cent, of water. The sample is 
further confirmed as one of a settled soap by the analysis, 
which shows no free caustic, the absence of much glycerol, 
and the low percentage of unsaponifiable matter. It is 
also possible to tell from the appearance of the sample whether 
the soap is a cold-process or a settled soap. Thus, if it has a 
broad, open texture resulting from the slow crystallization of 


TABLE VIII 

ANALYSES OF VARIOUS LAUNDRY SOAPS 


Ingredients 

1 

2 

3 

4 

5 

6 

7 

Per Cent, of Each Ingredient 

Water. 

26.30 

26.37 

29.68 

70.14 

71.59 

28.67 31.18 

Fatty anhydride . 

33.52 

30.77 

34.23 

7.20 

8.63 

41.69 

37.57 

Rosin anhydride . 

24.57 

28.89 

18.34 

none 

none 

15.06 

20.28 

Combined alkali . 

6.54 

7.21 

6.21 

1.33 

1.53 

6.87 

6.57 

Free NaOH .... 

trace 

none 

.04 

none 

.12 

none 

.02 

Free Na 2 C0 3 .... 

2.14 

2.53 

2.94 

7.87 

5.26 

2.23 

2.01 

Sodium silicate . . 

1.24 

1.47 

2.90 

none 

none 

none 

none 

Salt. 

.35 

.19 

.23 

11.28 

10.14 

.30 

.21 

Unsaponifiable . . 

3.08 


5.36 




1.08 

Insoluble. 

2.26 

2.49 

.07 


.23 

.48 

.08 


the sodium stearate in a menstruum of sodium oleate and 
sodium resinate, it is safe to say that the soap has not been 
crutched. If the soap is homogeneous in texture, with no 
marked crystallization, it has been crutched, in which process 
the texture arising from the slow cooling of the unfilled soap 
in the frames is broken up by the intimate mixing in the 
crutcher of the soap formed from fatty acids of different melting 
points. In Table VIII are given the analyses of various 
laundry soaps. 































66 


MANUFACTURE OF SOAP, PART 3 


CHEMICAL EXAMINATION OF REFINED GLYCERINE 

100. Determination of Salt. —To determine the 
amount of salt in a sample of refined glycerine, 100 cubic 
centimeters of the sample is diluted with 200 cubic centimeters 

N 

of water and titrated directly with — AgNOz using potassium 

chromate as an indicator. For all practical purposes, the 
weight of 100 cubic centimeters of glycerine is taken as 
126 grams. 

101. Determination of Asli. —To determine the ash 
present, weigh out 25 grams of glycerine on the coarse balance 
into a weighed platinum dish. Heat carefully to ignition 
and allow combustion to proceed. Expel all carbonaceous 
matter with a strong Bunsen-burner flame, taking care to lose 
no salt by volatilization or decrepitation. Cool and weigh 
on the fine balance. Calculate the percentage of ash as in the 
preceding case. 

102 . Higher Fatty Acids. —Pass a stream of nitrogen 
tetroxide through a portion of the glycerine that is diluted 
with twice its volume of distilled water and contained in a 
test tube. After this operation place the test tube on a 
steam bath and heat for 2 hours. Glycerine that is to be 
used for the manufacture of nitroglycerine should give no 
precipitate, either on dilution or later in the operation. 
Glycerine that will stand this test may be considered free 
from higher fatty acids. 

103 . Neutrality.—A glycerine may be considered neu¬ 
tral if, when 50 grams is diluted with twice its weight of dis¬ 
tilled water and a few drops of an alcoholic solution of phenol- 
phthalein are added, not more than 1 cubic centimeter 

£ N . 

of — sulphuric-acid or sodium-hydroxide solution is required 
to produce a change in color. 

104 . Specific Gravity. —Next to the quality of the 
glycerine, the specific gravity is the most important test, and 


MANUFACTURE OF SOAP, PART 3 


67 


this test requires care and skill for its accurate determination. 
The instrument used for making the specific-gravity deter¬ 
mination is called a picnometer. As shown by Fig. 13, it 
consists of a flask a the volume of which is known and which 
is fitted with a capillary tube b. This tube is capped by a 
glass cap c. The joint between the cap and the capillary 
tube is air-tight because of the fact that the outside of the 
tube b and the inside of c have been ground to a perfect fit. 
This is known as a ground-glass joint. The flask a also 
contains a thermometer d which is made to 
fit tightly by means of the ground-glass joint 
which it forms with a at e. 

The sample of glycerine in a glass-stoppered 
flask is cooled to a temperature of 10 to 12° C. 
and then transferred to the picnometer, which 
must be filled. The thermometer is then 
inserted and seated and the cap c removed. 

The picnometer is placed at once in a bath of 
ice water up to its neck. The bath is kept at 
a temperature of 12 to 13° C. by the ice and is 
well stirred to allow the temperature to rise 
slowly. The object is to get the temperature 
of the contents of the picnometer to equal the 
temperature of the bath at 15.5° C. When this 
equilibrium is reached, the excess of glycerine 
is carefully removed from the tip of the capillary 
tube and the cap put on. The picnometer is 
then taken from the bath, wiped off until abso¬ 
lutely dry, and allowed to stand in the balance room. When 
it has reached room temperature it is weighed. 

The total weight of the picnometer and glycerine minus the 
weight of the picnometer, gives the weight of a certain known 
volume of glycerine. The operation is now carried out with 
pure water under the same conditions. Then the weight of 
the glycerine divided by the weight of an equal volume of 
water at the same temperature gives the specific gravity of 
the glycerine. Table IX gives the specific gravities of aqueous 
solutions of glycerine as determined by Gerlach and Skalweit. 



Fig. 13 





























TABLE IX—SPECIFIC GRAVITY OF AQUEOUS SOLUTIONS OF 
CHEMICALLY PURE GLYCERINE 


Per 

Gerlach 

Skalweit 

Per 

Gerlach 

Skalweit 

Cent. 




Cent. 




Glycerol 

Sp. Gr. 

Sp. Gr. 

Sp. Gr. 

Glycerol 

Sp. Gr. 

Sp. Gr. 

Sp. Gr. 


15° C. 

20° C. 

15° C. 


15° C. 

20° C. 

15° 

0 

1.0000 

1.0000 

1.0000 

51 



1.1318 

1 



1.0024 

52 



1.1346 

2 



1.0048 

53 



1.1374 

3 



1.0072 

54 



1.1402 

4 



1.0096 

55 

1.1430 

1.4150 

1.1430 

5 



1.0120 

56 



1.1458 

6 



1.0144 

57 



1.1486 

7 



1.0168 

58 



1.1514 

8 



1.0192 

59 



1.1542 

9 



1.0216 

60 

1.1570 

1.1550 

1.1570 

10 

1.0245 

1.0235 

1.0240 

61 



1.1599 

11 



1.0265 

62 



1.1628 

12 



1.0290 

63 



1.1657 

13 



1.0315 

64 



1.1686 

14 



1.0340 

65 

1.1711 

1.1685 

1.1715 

15 



1.0365 

66 



1.1743 

16 



1.0390 

67 



1.1771 

17 



1.0415 

68 



1.1799 

18 



1.0440 

•69 



1.1827 

19 



1.0465 

70 

1.1850 

1.1820 

1.1855 

20 

1.0490 

1.0480 

1.0490 

71 

1.1878 

1.1847 

1.1882 

21 



1.0516 

72 

1.1906 

1.1874 

1.1909 

22 



1.0542 

73 

1.1934 

1.1901 

1.1936 

23 



1.0568 

74 

1.1962 

1.1928 

1.1963 

24 



1.0594 

75 

1.1990 

1.1955 

1.1990 

25 

1.0620 

1.0610 

1.0620 

76 

1.2018 

1.1982 

1.2017 

26 



1.0646 

77 

1.2046 

1.2009 

1.2044 

27 



1.0672 

78 

1.2074 

1.2036 

1.2071 

28 



1.0698 

79 

1.2102 

1.2063 

1.2098 

29 



1.0724 

80 

1.2130 

1.2090 

1.2125 

30 

1.0750 

1.0740 

1.0750 

81 

1.2157 

1.2117 

1.2152 

31 



1.0777 

82 

1.2184 

1.2144 

1.2179 

32 



1.0804 

83 

1.2211 

1.2171 

1.2206 

33 



1.0831 

84 

1.2238 

1.2198 

1.2233 

34 



1.0858 

85 

1.2265 

1.2225 

1.2260 

35 

1.0885 

1.0875 

1.0885 

86 

1.2292 

1.2252 

1.2287 

36 



1.0912 

87 

1.2319 

1.2279 

1.2314 

37 



1.0939 

88 

1.2346 

1.2306 

1.2341 

38 



1.0966 

89 

1.2373 

1.2333 

1.2368 

39 



1.0993 

90 

1.2400 

1.2360 

1.2395 

40 

1.1020 

1.1010 

1.1020 

91 

1.2425 

1.2386 

1.2421 

41 



1.1047 

92 

1.2451 

1.2412 

1.2447 

42 



1.1074 

93 

1.2476 

1.2438 

1.2473 

43 



1.1101 

94 

1.2501 

1.2464 

1.2499 

44 



1.1128 

95 

1.2526 

1.2490 

1.2525 

45 

1.1155 

1.1145 

1.1155 

96 

1.2552 

1.2516 

1.2550 

46 



1.1182 

97 

1.2577 

1.2542 

1.2575 

47 



1.1209 

98 

1.2602 

1.2568 

1.2600 

48 



1.1236 

99 

1.2628 

1.2594 

1.2625 

49 



1.1263 

100 

1.2653 

1.2620 

1.2650 

50 

1.1294 

1.1280 

1.1290 






G8 






























MANUFACTURE OF SOAP, PART 3 


69 


SPECIFICATIONS FOR GLYCERINE 

105 . The principal specifications for chemically pure 
glycerine are that it shall be water-white in color, of very 
slight odor, and have a specific gravity at 25° C. of 1.249; it 
must be neutral to litmus in a 1:20 water solution; it must not 
have a total residue on ignition of more than .0105 percent., 
of which not more than .007 per cent, of the whole must be 
mineral matter, and a total chlorine content of more than 
.001 per cent, calculated as sodium chloride. 

106 . The following specifications have been prepared 
by a large consumer for the purchase of dynamite glycerine: 

15.5° 

1. Specific gravity. Not less than 1.262 at ~ ~~o C. 

15.0 

2. Odor. Slight. No bad odor. 

3. Color. Not darker than straw color. 

4. Acidity. When 50 cubic centimeters of the glycerine 
plus 10 cubic centimeters of distilled water free from carbon 
dioxide are mixed and about J cubic centimeter of phenol- 
pthalein indicator (5 g. per liter of 50-per-cent, alcohol) used, 
it shall not require more than .3 cubic centimeter of normal 
hydrochloric acid nor more than .3 cubic centimeter of 
normal sodium-hydroxide solution for neutralization. 

5. Ash not over .1 per cent. 

6. Chlorine. Not over .01 per cent, chlorine as calculated 
from a volumetric determination of the chlorine in the aqueous 
solution of the residue left on ignition. 

7. Nitration and separation. When 15 grams are nitrated 
in a glass vessel with 70 cubic centimeters of a mixture 
consisting of 37-per-cent, pure nitric acid of 1.5 specific 
gravity and 63-per-cent, pure sulphuric acid of 1.845 specific 
gravity, at a temperature not allowed to exceed 20° C., and 
the whole poured into a glass cylinder of 1J inches internal 
diameter, the nitroglycerine should separate so that the line 
of demarcation will be clear, and there should be practically 
no so-called flocculent matter present. 
























.X 



































